A description of some of the currently available audio decoders
follows.
AC-3 audio decoder.
This decoder implements part of ATSC A/52:2010 and ETSI TS 102
366, as well as the undocumented RealAudio 3 (a.k.a. dnet).
AC-3 Decoder Options
- -drc_scale
value
- Dynamic Range Scale Factor. The factor to apply to dynamic range values
from the AC-3 stream. This factor is applied exponentially. There are 3
notable scale factor ranges:
- drc_scale ==
0
- DRC disabled. Produces full range audio.
- 0 < drc_scale <= 1
- DRC enabled. Applies a fraction of the stream DRC value. Audio
reproduction is between full range and full compression.
- drc_scale
> 1
- DRC enabled. Applies drc_scale asymmetrically. Loud sounds are fully
compressed. Soft sounds are enhanced.
FLAC audio decoder.
This decoder aims to implement the complete FLAC specification
from Xiph.
FLAC Decoder options
- -use_buggy_lpc
- The lavc FLAC encoder used to produce buggy streams with high lpc values
(like the default value). This option makes it possible to decode such
streams correctly by using lavc's old buggy lpc logic for decoding.
Internal wave synthesizer.
This decoder generates wave patterns according to predefined
sequences. Its use is purely internal and the format of the data it accepts
is not publicly documented.
libcelt decoder wrapper.
libcelt allows libavcodec to decode the Xiph CELT ultra-low delay
audio codec. Requires the presence of the libcelt headers and library during
configuration. You need to explicitly configure the build with
"--enable-libcelt".
libgsm decoder wrapper.
libgsm allows libavcodec to decode the GSM full rate audio codec.
Requires the presence of the libgsm headers and library during
configuration. You need to explicitly configure the build with
"--enable-libgsm".
This decoder supports both the ordinary GSM and the Microsoft
variant.
libilbc decoder wrapper.
libilbc allows libavcodec to decode the Internet Low Bitrate Codec
(iLBC) audio codec. Requires the presence of the libilbc headers and library
during configuration. You need to explicitly configure the build with
"--enable-libilbc".
Options
The following option is supported by the libilbc wrapper.
- enhance
- Enable the enhancement of the decoded audio when set to 1. The default
value is 0 (disabled).
libopencore-amrnb decoder wrapper.
libopencore-amrnb allows libavcodec to decode the Adaptive
Multi-Rate Narrowband audio codec. Using it requires the presence of the
libopencore-amrnb headers and library during configuration. You need to
explicitly configure the build with
"--enable-libopencore-amrnb".
An FFmpeg native decoder for AMR-NB exists, so users can decode
AMR-NB without this library.
libopencore-amrwb decoder wrapper.
libopencore-amrwb allows libavcodec to decode the Adaptive
Multi-Rate Wideband audio codec. Using it requires the presence of the
libopencore-amrwb headers and library during configuration. You need to
explicitly configure the build with
"--enable-libopencore-amrwb".
An FFmpeg native decoder for AMR-WB exists, so users can decode
AMR-WB without this library.
libopus decoder wrapper.
libopus allows libavcodec to decode the Opus Interactive Audio
Codec. Requires the presence of the libopus headers and library during
configuration. You need to explicitly configure the build with
"--enable-libopus".
An FFmpeg native decoder for Opus exists, so users can decode Opus
without this library.
A description of some of the currently available audio encoders
follows.
Advanced Audio Coding (AAC) encoder.
This encoder is the default AAC encoder, natively implemented into
FFmpeg.
Options
- b
- Set bit rate in bits/s. Setting this automatically activates constant bit
rate (CBR) mode. If this option is unspecified it is set to 128kbps.
- q
- Set quality for variable bit rate (VBR) mode. This option is valid only
using the ffmpeg command-line tool. For library interface users,
use global_quality.
- cutoff
- Set cutoff frequency. If unspecified will allow the encoder to dynamically
adjust the cutoff to improve clarity on low bitrates.
- aac_coder
- Set AAC encoder coding method. Possible values:
- twoloop
- Two loop searching (TLS) method.
This method first sets quantizers depending on band thresholds
and then tries to find an optimal combination by adding or subtracting a
specific value from all quantizers and adjusting some individual
quantizer a little. Will tune itself based on whether aac_is,
aac_ms and aac_pns are enabled.
- anmr
- Average noise to mask ratio (ANMR) trellis-based solution.
This is an experimental coder which currently produces a lower
quality, is more unstable and is slower than the default twoloop coder
but has potential. Currently has no support for the aac_is or
aac_pns options. Not currently recommended.
- fast
- Constant quantizer method.
Uses a cheaper version of twoloop algorithm that doesn't try
to do as many clever adjustments. Worse with low bitrates (less than
64kbps), but is better and much faster at higher bitrates. This is the
default choice for a coder
- aac_ms
- Sets mid/side coding mode. The default value of "auto" will
automatically use M/S with bands which will benefit from such coding. Can
be forced for all bands using the value "enable", which is
mainly useful for debugging or disabled using "disable".
- aac_is
- Sets intensity stereo coding tool usage. By default, it's enabled and will
automatically toggle IS for similar pairs of stereo bands if it's
beneficial. Can be disabled for debugging by setting the value to
"disable".
- aac_pns
- Uses perceptual noise substitution to replace low entropy high frequency
bands with imperceptible white noise during the decoding process. By
default, it's enabled, but can be disabled for debugging purposes by using
"disable".
- aac_tns
- Enables the use of a multitap FIR filter which spans through the high
frequency bands to hide quantization noise during the encoding process and
is reverted by the decoder. As well as decreasing unpleasant artifacts in
the high range this also reduces the entropy in the high bands and allows
for more bits to be used by the mid-low bands. By default it's enabled but
can be disabled for debugging by setting the option to
"disable".
- aac_ltp
- Enables the use of the long term prediction extension which increases
coding efficiency in very low bandwidth situations such as encoding of
voice or solo piano music by extending constant harmonic peaks in bands
throughout frames. This option is implied by profile:a aac_low and is
incompatible with aac_pred. Use in conjunction with -ar to decrease
the samplerate.
- aac_pred
- Enables the use of a more traditional style of prediction where the
spectral coefficients transmitted are replaced by the difference of the
current coefficients minus the previous "predicted"
coefficients. In theory and sometimes in practice this can improve quality
for low to mid bitrate audio. This option implies the aac_main profile and
is incompatible with aac_ltp.
- profile
- Sets the encoding profile, possible values:
- aac_low
- The default, AAC "Low-complexity" profile. Is the most
compatible and produces decent quality.
- mpeg2_aac_low
- Equivalent to "-profile:a aac_low -aac_pns
0". PNS was introduced with the MPEG4 specifications.
- aac_ltp
- Long term prediction profile, is enabled by and will enable the
aac_ltp option. Introduced in MPEG4.
- aac_main
- Main-type prediction profile, is enabled by and will enable the
aac_pred option. Introduced in MPEG2.
If this option is unspecified it is set to aac_low.
AC-3 audio encoders.
These encoders implement part of ATSC A/52:2010 and ETSI TS 102
366, as well as the undocumented RealAudio 3 (a.k.a. dnet).
The ac3 encoder uses floating-point math, while the
ac3_fixed encoder only uses fixed-point integer math. This does not
mean that one is always faster, just that one or the other may be better
suited to a particular system. The floating-point encoder will generally
produce better quality audio for a given bitrate. The ac3_fixed
encoder is not the default codec for any of the output formats, so it must
be specified explicitly using the option "-acodec
ac3_fixed" in order to use it.
AC-3 Metadata
The AC-3 metadata options are used to set parameters that describe
the audio, but in most cases do not affect the audio encoding itself. Some
of the options do directly affect or influence the decoding and playback of
the resulting bitstream, while others are just for informational purposes. A
few of the options will add bits to the output stream that could otherwise
be used for audio data, and will thus affect the quality of the output.
Those will be indicated accordingly with a note in the option list
below.
These parameters are described in detail in several
publicly-available documents.
- *<<http://www.atsc.org/cms/standards/a_52-2010.pdf>>
- *<<http://www.atsc.org/cms/standards/a_54a_with_corr_1.pdf>>
- *<<http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf>>
- *<<http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf>>
Metadata Control Options
- -per_frame_metadata
boolean
- Allow Per-Frame Metadata. Specifies if the encoder should check for
changing metadata for each frame.
- 0
- The metadata values set at initialization will be used for every frame in
the stream. (default)
- 1
- Metadata values can be changed before encoding each frame.
Downmix Levels
- -center_mixlev
level
- Center Mix Level. The amount of gain the decoder should apply to the
center channel when downmixing to stereo. This field will only be written
to the bitstream if a center channel is present. The value is specified as
a scale factor. There are 3 valid values:
- 0.707
- Apply -3dB gain
- 0.595
- Apply -4.5dB gain (default)
- 0.500
- Apply -6dB gain
- -surround_mixlev
level
- Surround Mix Level. The amount of gain the decoder should apply to the
surround channel(s) when downmixing to stereo. This field will only be
written to the bitstream if one or more surround channels are present. The
value is specified as a scale factor. There are 3 valid values:
- 0.707
- Apply -3dB gain
- 0.500
- Apply -6dB gain (default)
- 0.000
- Silence Surround Channel(s)
Audio Production Information
Audio Production Information is optional information describing
the mixing environment. Either none or both of the fields are written to the
bitstream.
- -mixing_level
number
- Mixing Level. Specifies peak sound pressure level (SPL) in the production
environment when the mix was mastered. Valid values are 80 to 111, or -1
for unknown or not indicated. The default value is -1, but that value
cannot be used if the Audio Production Information is written to the
bitstream. Therefore, if the "room_type"
option is not the default value, the
"mixing_level" option must not be
-1.
- -room_type
type
- Room Type. Describes the equalization used during the final mixing session
at the studio or on the dubbing stage. A large room is a dubbing stage
with the industry standard X-curve equalization; a small room has flat
equalization. This field will not be written to the bitstream if both the
"mixing_level" option and the
"room_type" option have the default
values.
Other Metadata Options
- -copyright
boolean
- Copyright Indicator. Specifies whether a copyright exists for this
audio.
- 0
- off
- No Copyright Exists (default)
- 1
- on
- Copyright Exists
- -dialnorm
value
- Dialogue Normalization. Indicates how far the average dialogue level of
the program is below digital 100% full scale (0 dBFS). This parameter
determines a level shift during audio reproduction that sets the average
volume of the dialogue to a preset level. The goal is to match volume
level between program sources. A value of -31dB will result in no volume
level change, relative to the source volume, during audio reproduction.
Valid values are whole numbers in the range -31 to -1, with -31 being the
default.
- -dsur_mode
mode
- Dolby Surround Mode. Specifies whether the stereo signal uses Dolby
Surround (Pro Logic). This field will only be written to the bitstream if
the audio stream is stereo. Using this option does NOT mean the
encoder will actually apply Dolby Surround processing.
- 0
- notindicated
- Not Indicated (default)
- 1
- off
- Not Dolby Surround Encoded
- 2
- on
- Dolby Surround Encoded
- -original
boolean
- Original Bit Stream Indicator. Specifies whether this audio is from the
original source and not a copy.
- 0
- off
- Not Original Source
- 1
- on
- Original Source (default)
Extended Bitstream Information
The extended bitstream options are part of the Alternate Bit
Stream Syntax as specified in Annex D of the A/52:2010 standard. It is
grouped into 2 parts. If any one parameter in a group is specified, all
values in that group will be written to the bitstream. Default values are
used for those that are written but have not been specified. If the mixing
levels are written, the decoder will use these values instead of the ones
specified in the "center_mixlev" and
"surround_mixlev" options if it supports
the Alternate Bit Stream Syntax.
Extended Bitstream Information - Part 1
- -dmix_mode
mode
- Preferred Stereo Downmix Mode. Allows the user to select either Lt/Rt
(Dolby Surround) or Lo/Ro (normal stereo) as the preferred stereo downmix
mode.
- 0
- notindicated
- Not Indicated (default)
- 1
- ltrt
- Lt/Rt Downmix Preferred
- 2
- loro
- Lo/Ro Downmix Preferred
- -ltrt_cmixlev
level
- Lt/Rt Center Mix Level. The amount of gain the decoder should apply to the
center channel when downmixing to stereo in Lt/Rt mode.
- 1.414
- Apply +3dB gain
- 1.189
- Apply +1.5dB gain
- 1.000
- Apply 0dB gain
- 0.841
- Apply -1.5dB gain
- 0.707
- Apply -3.0dB gain
- 0.595
- Apply -4.5dB gain (default)
- 0.500
- Apply -6.0dB gain
- 0.000
- Silence Center Channel
- -ltrt_surmixlev
level
- Lt/Rt Surround Mix Level. The amount of gain the decoder should apply to
the surround channel(s) when downmixing to stereo in Lt/Rt mode.
- 0.841
- Apply -1.5dB gain
- 0.707
- Apply -3.0dB gain
- 0.595
- Apply -4.5dB gain
- 0.500
- Apply -6.0dB gain (default)
- 0.000
- Silence Surround Channel(s)
- -loro_cmixlev
level
- Lo/Ro Center Mix Level. The amount of gain the decoder should apply to the
center channel when downmixing to stereo in Lo/Ro mode.
- 1.414
- Apply +3dB gain
- 1.189
- Apply +1.5dB gain
- 1.000
- Apply 0dB gain
- 0.841
- Apply -1.5dB gain
- 0.707
- Apply -3.0dB gain
- 0.595
- Apply -4.5dB gain (default)
- 0.500
- Apply -6.0dB gain
- 0.000
- Silence Center Channel
- -loro_surmixlev
level
- Lo/Ro Surround Mix Level. The amount of gain the decoder should apply to
the surround channel(s) when downmixing to stereo in Lo/Ro mode.
- 0.841
- Apply -1.5dB gain
- 0.707
- Apply -3.0dB gain
- 0.595
- Apply -4.5dB gain
- 0.500
- Apply -6.0dB gain (default)
- 0.000
- Silence Surround Channel(s)
Extended Bitstream Information - Part 2
- -dsurex_mode
mode
- Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround
EX (7.1 matrixed to 5.1). Using this option does NOT mean the
encoder will actually apply Dolby Surround EX processing.
- 0
- notindicated
- Not Indicated (default)
- 1
- on
- Dolby Surround EX Off
- 2
- off
- Dolby Surround EX On
- -dheadphone_mode
mode
- Dolby Headphone Mode. Indicates whether the stream uses Dolby Headphone
encoding (multi-channel matrixed to 2.0 for use with headphones). Using
this option does NOT mean the encoder will actually apply Dolby
Headphone processing.
- 0
- notindicated
- Not Indicated (default)
- 1
- on
- Dolby Headphone Off
- 2
- off
- Dolby Headphone On
- -ad_conv_type
type
- A/D Converter Type. Indicates whether the audio has passed through HDCD
A/D conversion.
- 0
- standard
- Standard A/D Converter (default)
- 1
- hdcd
- HDCD A/D Converter
Other AC-3 Encoding Options
- -stereo_rematrixing
boolean
- Stereo Rematrixing. Enables/Disables use of rematrixing for stereo input.
This is an optional AC-3 feature that increases quality by selectively
encoding the left/right channels as mid/side. This option is enabled by
default, and it is highly recommended that it be left as enabled except
for testing purposes.
- cutoff
frequency
- Set lowpass cutoff frequency. If unspecified, the encoder selects a
default determined by various other encoding parameters.
Floating-Point-Only AC-3 Encoding Options
These options are only valid for the floating-point encoder and do
not exist for the fixed-point encoder due to the corresponding features not
being implemented in fixed-point.
- -channel_coupling
boolean
- Enables/Disables use of channel coupling, which is an optional AC-3
feature that increases quality by combining high frequency information
from multiple channels into a single channel. The per-channel high
frequency information is sent with less accuracy in both the frequency and
time domains. This allows more bits to be used for lower frequencies while
preserving enough information to reconstruct the high frequencies. This
option is enabled by default for the floating-point encoder and should
generally be left as enabled except for testing purposes or to increase
encoding speed.
- -1
- auto
- Selected by Encoder (default)
- 0
- off
- Disable Channel Coupling
- 1
- on
- Enable Channel Coupling
- -cpl_start_band
number
- Coupling Start Band. Sets the channel coupling start band, from 1 to 15.
If a value higher than the bandwidth is used, it will be reduced to 1 less
than the coupling end band. If auto is used, the start band will be
determined by the encoder based on the bit rate, sample rate, and channel
layout. This option has no effect if channel coupling is disabled.
- -1
- auto
- Selected by Encoder (default)
FLAC (Free Lossless Audio Codec) Encoder
Options
The following options are supported by FFmpeg's flac encoder.
- compression_level
- Sets the compression level, which chooses defaults for many other options
if they are not set explicitly. Valid values are from 0 to 12, 5 is the
default.
- frame_size
- Sets the size of the frames in samples per channel.
- lpc_coeff_precision
- Sets the LPC coefficient precision, valid values are from 1 to 15, 15 is
the default.
- lpc_type
- Sets the first stage LPC algorithm
- lpc_passes
- Number of passes to use for Cholesky factorization during LPC
analysis
- min_partition_order
- The minimum partition order
- max_partition_order
- The maximum partition order
- prediction_order_method
- ch_mode
- Channel mode
- exact_rice_parameters
- Chooses if rice parameters are calculated exactly or approximately. if set
to 1 then they are chosen exactly, which slows the code down slightly and
improves compression slightly.
- multi_dim_quant
- Multi Dimensional Quantization. If set to 1 then a 2nd stage LPC algorithm
is applied after the first stage to finetune the coefficients. This is
quite slow and slightly improves compression.
Opus encoder.
This is a native FFmpeg encoder for the Opus format. Currently its
in development and only implements the CELT part of the codec. Its quality
is usually worse and at best is equal to the libopus encoder.
Options
- b
- Set bit rate in bits/s. If unspecified it uses the number of channels and
the layout to make a good guess.
- opus_delay
- Sets the maximum delay in milliseconds. Lower delays than 20ms will very
quickly decrease quality.
libfdk-aac AAC (Advanced Audio Coding) encoder wrapper.
The libfdk-aac library is based on the Fraunhofer FDK AAC code
from the Android project.
Requires the presence of the libfdk-aac headers and library during
configuration. You need to explicitly configure the build with
"--enable-libfdk-aac". The library is also
incompatible with GPL, so if you allow the use of GPL, you should configure
with "--enable-gpl --enable-nonfree
--enable-libfdk-aac".
This encoder has support for the AAC-HE profiles.
VBR encoding, enabled through the vbr or flags
+qscale options, is experimental and only works with some
combinations of parameters.
Support for encoding 7.1 audio is only available with libfdk-aac
0.1.3 or higher.
For more information see the fdk-aac project at
<http://sourceforge.net/p/opencore-amr/fdk-aac/>.
Options
The following options are mapped on the shared FFmpeg codec
options.
- b
- Set bit rate in bits/s. If the bitrate is not explicitly specified, it is
automatically set to a suitable value depending on the selected profile.
In case VBR mode is enabled the option is ignored.
- ar
- Set audio sampling rate (in Hz).
- channels
- Set the number of audio channels.
- flags
+qscale
- Enable fixed quality, VBR (Variable Bit Rate) mode. Note that VBR is
implicitly enabled when the vbr value is positive.
- cutoff
- Set cutoff frequency. If not specified (or explicitly set to 0) it will
use a value automatically computed by the library. Default value is
0.
- profile
- Set audio profile.
The following profiles are recognized:
- aac_low
- Low Complexity AAC (LC)
- aac_he
- High Efficiency AAC (HE-AAC)
- aac_he_v2
- High Efficiency AAC version 2 (HE-AACv2)
- aac_ld
- Low Delay AAC (LD)
- aac_eld
- Enhanced Low Delay AAC (ELD)
If not specified it is set to aac_low.
The following are private options of the libfdk_aac encoder.
- afterburner
- Enable afterburner feature if set to 1, disabled if set to 0. This
improves the quality but also the required processing power.
Default value is 1.
- eld_sbr
- Enable SBR (Spectral Band Replication) for ELD if set to 1, disabled if
set to 0.
Default value is 0.
- eld_v2
- Enable ELDv2 (LD-MPS extension for ELD stereo signals) for ELDv2 if set to
1, disabled if set to 0.
Note that option is available when fdk-aac version
(AACENCODER_LIB_VL0.AACENCODER_LIB_VL1.AACENCODER_LIB_VL2) >
(4.0.0).
Default value is 0.
- signaling
- Set SBR/PS signaling style.
It can assume one of the following values:
- default
- choose signaling implicitly (explicit hierarchical by default, implicit if
global header is disabled)
- implicit
- implicit backwards compatible signaling
- explicit_sbr
- explicit SBR, implicit PS signaling
- explicit_hierarchical
- explicit hierarchical signaling
Default value is default.
- latm
- Output LATM/LOAS encapsulated data if set to 1, disabled if set to 0.
Default value is 0.
- Set StreamMuxConfig and PCE repetition period (in frames) for sending
in-band configuration buffers within LATM/LOAS transport layer.
Must be a 16-bits non-negative integer.
Default value is 0.
- vbr
- Set VBR mode, from 1 to 5. 1 is lowest quality (though still pretty good)
and 5 is highest quality. A value of 0 will disable VBR, and CBR (Constant
Bit Rate) is enabled.
Currently only the aac_low profile supports VBR
encoding.
VBR modes 1-5 correspond to roughly the following average bit
rates:
- 1
- 32 kbps/channel
- 2
- 40 kbps/channel
- 3
- 48-56 kbps/channel
- 4
- 64 kbps/channel
- 5
- about 80-96 kbps/channel
Examples
LAME (Lame Ain't an MP3 Encoder) MP3 encoder wrapper.
Requires the presence of the libmp3lame headers and library during
configuration. You need to explicitly configure the build with
"--enable-libmp3lame".
See libshine for a fixed-point MP3 encoder, although with a
lower quality.
Options
The following options are supported by the libmp3lame wrapper. The
lame-equivalent of the options are listed in parentheses.
- b
(-b)
- Set bitrate expressed in bits/s for CBR or ABR. LAME
"bitrate" is expressed in
kilobits/s.
- q
(-V)
- Set constant quality setting for VBR. This option is valid only using the
ffmpeg command-line tool. For library interface users, use
global_quality.
- compression_level
(-q)
- Set algorithm quality. Valid arguments are integers in the 0-9 range, with
0 meaning highest quality but slowest, and 9 meaning fastest while
producing the worst quality.
- cutoff
(--lowpass)
- Set lowpass cutoff frequency. If unspecified, the encoder dynamically
adjusts the cutoff.
- reservoir
- Enable use of bit reservoir when set to 1. Default value is 1. LAME has
this enabled by default, but can be overridden by use --nores
option.
- joint_stereo
(-m j)
- Enable the encoder to use (on a frame by frame basis) either L/R stereo or
mid/side stereo. Default value is 1.
- abr
(--abr)
- Enable the encoder to use ABR when set to 1. The lame --abr
sets the target bitrate, while this options only tells FFmpeg to use ABR
still relies on b to set bitrate.
OpenCORE Adaptive Multi-Rate Narrowband encoder.
Requires the presence of the libopencore-amrnb headers and library
during configuration. You need to explicitly configure the build with
"--enable-libopencore-amrnb
--enable-version3".
This is a mono-only encoder. Officially it only supports 8000Hz
sample rate, but you can override it by setting strict to
unofficial or lower.
Options
- b
- Set bitrate in bits per second. Only the following bitrates are supported,
otherwise libavcodec will round to the nearest valid bitrate.
- 4750
- 5150
- 5900
- 6700
- 7400
- 7950
- 10200
- 12200
- dtx
- Allow discontinuous transmission (generate comfort noise) when set to 1.
The default value is 0 (disabled).
libopus Opus Interactive Audio Codec encoder wrapper.
Requires the presence of the libopus headers and library during
configuration. You need to explicitly configure the build with
"--enable-libopus".
Option Mapping
Most libopus options are modelled after the opusenc utility
from opus-tools. The following is an option mapping chart describing options
supported by the libopus wrapper, and their opusenc-equivalent in
parentheses.
- b
(bitrate)
- Set the bit rate in bits/s. FFmpeg's b option is expressed in
bits/s, while opusenc's bitrate in kilobits/s.
- vbr
(vbr, hard-cbr, and
cvbr)
- Set VBR mode. The FFmpeg vbr option has the following valid
arguments, with the opusenc equivalent options in parentheses:
- compression_level
(comp)
- Set encoding algorithm complexity. Valid options are integers in the 0-10
range. 0 gives the fastest encodes but lower quality, while 10 gives the
highest quality but slowest encoding. The default is 10.
- frame_duration
(framesize)
- Set maximum frame size, or duration of a frame in milliseconds. The
argument must be exactly the following: 2.5, 5, 10, 20, 40, 60. Smaller
frame sizes achieve lower latency but less quality at a given bitrate.
Sizes greater than 20ms are only interesting at fairly low bitrates. The
default is 20ms.
- packet_loss
(expect-loss)
- Set expected packet loss percentage. The default is 0.
- application
(N.A.)
- Set intended application type. Valid options are listed below:
- voip
- Favor improved speech intelligibility.
- audio
- Favor faithfulness to the input (the default).
- lowdelay
- Restrict to only the lowest delay modes.
- cutoff
(N.A.)
- Set cutoff bandwidth in Hz. The argument must be exactly one of the
following: 4000, 6000, 8000, 12000, or 20000, corresponding to narrowband,
mediumband, wideband, super wideband, and fullband respectively. The
default is 0 (cutoff disabled).
- mapping_family
(mapping_family)
- Set channel mapping family to be used by the encoder. The default value of
-1 uses mapping family 0 for mono and stereo inputs, and mapping family 1
otherwise. The default also disables the surround masking and LFE
bandwidth optimzations in libopus, and requires that the input contains 8
channels or fewer.
Other values include 0 for mono and stereo, 1 for surround
sound with masking and LFE bandwidth optimizations, and 255 for
independent streams with an unspecified channel layout.
- apply_phase_inv
(N.A.) (requires libopus >= 1.2)
- If set to 0, disables the use of phase inversion for intensity stereo,
improving the quality of mono downmixes, but slightly reducing normal
stereo quality. The default is 1 (phase inversion enabled).
Shine Fixed-Point MP3 encoder wrapper.
Shine is a fixed-point MP3 encoder. It has a far better
performance on platforms without an FPU, e.g. armel CPUs, and some phones
and tablets. However, as it is more targeted on performance than quality, it
is not on par with LAME and other production-grade encoders quality-wise.
Also, according to the project's homepage, this encoder may not be free of
bugs as the code was written a long time ago and the project was dead for at
least 5 years.
This encoder only supports stereo and mono input. This is also
CBR-only.
The original project (last updated in early 2007) is at
<http://sourceforge.net/projects/libshine-fxp/>. We only
support the updated fork by the Savonet/Liquidsoap project at
<https://github.com/savonet/shine>.
Requires the presence of the libshine headers and library during
configuration. You need to explicitly configure the build with
"--enable-libshine".
See also libmp3lame.
Options
The following options are supported by the libshine wrapper. The
shineenc-equivalent of the options are listed in parentheses.
- b
(-b)
- Set bitrate expressed in bits/s for CBR. shineenc -b option
is expressed in kilobits/s.
TwoLAME MP2 encoder wrapper.
Requires the presence of the libtwolame headers and library during
configuration. You need to explicitly configure the build with
"--enable-libtwolame".
Options
The following options are supported by the libtwolame wrapper. The
twolame-equivalent options follow the FFmpeg ones and are in
parentheses.
- b
(-b)
- Set bitrate expressed in bits/s for CBR. twolame b option is
expressed in kilobits/s. Default value is 128k.
- q
(-V)
- Set quality for experimental VBR support. Maximum value range is from -50
to 50, useful range is from -10 to 10. The higher the value, the better
the quality. This option is valid only using the ffmpeg
command-line tool. For library interface users, use
global_quality.
- mode
(--mode)
- Set the mode of the resulting audio. Possible values:
- psymodel
(--psyc-mode)
- Set psychoacoustic model to use in encoding. The argument must be an
integer between -1 and 4, inclusive. The higher the value, the better the
quality. The default value is 3.
- energy_levels
(--energy)
- Enable energy levels extensions when set to 1. The default value is 0
(disabled).
- error_protection
(--protect)
- Enable CRC error protection when set to 1. The default value is 0
(disabled).
- copyright
(--copyright)
- Set MPEG audio copyright flag when set to 1. The default value is 0
(disabled).
- original
(--original)
- Set MPEG audio original flag when set to 1. The default value is 0
(disabled).
VisualOn Adaptive Multi-Rate Wideband encoder.
Requires the presence of the libvo-amrwbenc headers and library
during configuration. You need to explicitly configure the build with
"--enable-libvo-amrwbenc
--enable-version3".
This is a mono-only encoder. Officially it only supports 16000Hz
sample rate, but you can override it by setting strict to
unofficial or lower.
Options
- b
- Set bitrate in bits/s. Only the following bitrates are supported,
otherwise libavcodec will round to the nearest valid bitrate.
- 6600
- 8850
- 12650
- 14250
- 15850
- 18250
- 19850
- 23050
- 23850
- dtx
- Allow discontinuous transmission (generate comfort noise) when set to 1.
The default value is 0 (disabled).
libvorbis encoder wrapper.
Requires the presence of the libvorbisenc headers and library
during configuration. You need to explicitly configure the build with
"--enable-libvorbis".
Options
The following options are supported by the libvorbis wrapper. The
oggenc-equivalent of the options are listed in parentheses.
To get a more accurate and extensive documentation of the
libvorbis options, consult the libvorbisenc's and oggenc's
documentations. See <http://xiph.org/vorbis/>,
<http://wiki.xiph.org/Vorbis-tools>, and oggenc(1).
- b
(-b)
- Set bitrate expressed in bits/s for ABR. oggenc -b is
expressed in kilobits/s.
- q
(-q)
- Set constant quality setting for VBR. The value should be a float number
in the range of -1.0 to 10.0. The higher the value, the better the
quality. The default value is 3.0.
This option is valid only using the ffmpeg command-line
tool. For library interface users, use global_quality.
- cutoff
(--advanced-encode-option lowpass_frequency=N)
- Set cutoff bandwidth in Hz, a value of 0 disables cutoff. oggenc's
related option is expressed in kHz. The default value is 0 (cutoff
disabled).
- minrate
(-m)
- Set minimum bitrate expressed in bits/s. oggenc -m is
expressed in kilobits/s.
- maxrate
(-M)
- Set maximum bitrate expressed in bits/s. oggenc -M is
expressed in kilobits/s. This only has effect on ABR mode.
- iblock
(--advanced-encode-option impulse_noisetune=N)
- Set noise floor bias for impulse blocks. The value is a float number from
-15.0 to 0.0. A negative bias instructs the encoder to pay special
attention to the crispness of transients in the encoded audio. The
tradeoff for better transient response is a higher bitrate.
A wrapper providing WavPack encoding through libwavpack.
Only lossless mode using 32-bit integer samples is supported
currently.
Requires the presence of the libwavpack headers and library during
configuration. You need to explicitly configure the build with
"--enable-libwavpack".
Note that a libavcodec-native encoder for the WavPack codec exists
so users can encode audios with this codec without using this encoder. See
wavpackenc.
Options
wavpack command line utility's corresponding options are
listed in parentheses, if any.
- frame_size
(--blocksize)
- Default is 32768.
- compression_level
- Set speed vs. compression tradeoff. Acceptable arguments are listed
below:
- 0 (-f)
- Fast mode.
- 1
- Normal (default) settings.
- 2 (-h)
- High quality.
- 3 (-hh)
- Very high quality.
- 4-8 (-hh -xEXTRAPROC)
- Same as 3, but with extra processing enabled.
4 is the same as -x2 and 8 is the same as
-x6.
Motion JPEG encoder.
Options
- huffman
- Set the huffman encoding strategy. Possible values:
- default
- Use the default huffman tables. This is the default strategy.
- optimal
- Compute and use optimal huffman tables.
WavPack lossless audio encoder.
This is a libavcodec-native WavPack encoder. There is also an
encoder based on libwavpack, but there is virtually no reason to use that
encoder.
See also libwavpack.
Options
The equivalent options for wavpack command line utility are
listed in parentheses.
Shared options
The following shared options are effective for this encoder. Only
special notes about this particular encoder will be documented here. For the
general meaning of the options, see the Codec Options chapter.
- frame_size
(--blocksize)
- For this encoder, the range for this option is between 128 and 131072.
Default is automatically decided based on sample rate and number of
channel.
For the complete formula of calculating default, see
libavcodec/wavpackenc.c.
- compression_level
(-f, -h, -hh, and
-x)
- This option's syntax is consistent with libwavpack's.
Private options
- joint_stereo
(-j)
- Set whether to enable joint stereo. Valid values are:
- on
(1)
- Force mid/side audio encoding.
- off
(0)
- Force left/right audio encoding.
- auto
- Let the encoder decide automatically.
- optimize_mono
- Set whether to enable optimization for mono. This option is only effective
for non-mono streams. Available values:
A description of some of the currently available video encoders
follows.
Vidvox Hap video encoder.
Options
- format
integer
- Specifies the Hap format to encode.
- chunks
integer
- Specifies the number of chunks to split frames into, between 1 and 64.
This permits multithreaded decoding of large frames, potentially at the
cost of data-rate. The encoder may modify this value to divide frames
evenly.
Default value is 1.
- compressor
integer
- Specifies the second-stage compressor to use. If set to none,
chunks will be limited to 1, as chunked uncompressed frames offer
no benefit.
The native jpeg 2000 encoder is lossy by default, the
"-q:v" option can be used to set the
encoding quality. Lossless encoding can be selected with
"-pred 1".
Options
- format
- Can be set to either "j2k" or
"jp2" (the default) that makes it
possible to store non-rgb pix_fmts.
rav1e AV1 encoder wrapper.
Requires the presence of the rav1e headers and library during
configuration. You need to explicitly configure the build with
"--enable-librav1e".
Options
- qmax
- Sets the maximum quantizer to use when using bitrate mode.
- qmin
- Sets the minimum quantizer to use when using bitrate mode.
- qp
- Uses quantizer mode to encode at the given quantizer (0-255).
- speed
- Selects the speed preset (0-10) to encode with.
- tiles
- Selects how many tiles to encode with.
- tile-rows
- Selects how many rows of tiles to encode with.
- tile-columns
- Selects how many columns of tiles to encode with.
- rav1e-params
- Set rav1e options using a list of key=value pairs separated
by ":". See rav1e --help for a list of options.
For example to specify librav1e encoding options with
-rav1e-params:
ffmpeg -i input -c:v librav1e -b:v 500K -rav1e-params speed=5:low_latency=true output.mp4
libaom AV1 encoder wrapper.
Requires the presence of the libaom headers and library during
configuration. You need to explicitly configure the build with
"--enable-libaom".
Options
The wrapper supports the following standard libavcodec
options:
- b
- Set bitrate target in bits/second. By default this will use
variable-bitrate mode. If maxrate and minrate are also set
to the same value then it will use constant-bitrate mode, otherwise if
crf is set as well then it will use constrained-quality mode.
- g keyint_min
- Set key frame placement. The GOP size sets the maximum distance between
key frames; if zero the output stream will be intra-only. The minimum
distance is ignored unless it is the same as the GOP size, in which case
key frames will always appear at a fixed interval. Not set by default, so
without this option the library has completely free choice about where to
place key frames.
- qmin qmax
- Set minimum/maximum quantisation values. Valid range is from 0 to 63
(warning: this does not match the quantiser values actually used by AV1 -
divide by four to map real quantiser values to this range). Defaults to
min/max (no constraint).
- minrate maxrate
bufsize rc_init_occupancy
- Set rate control buffering parameters. Not used if not set - defaults to
unconstrained variable bitrate.
- threads
- Set the number of threads to use while encoding. This may require the
tiles or row-mt options to also be set to actually use the
specified number of threads fully. Defaults to the number of hardware
threads supported by the host machine.
- profile
- Set the encoding profile. Defaults to using the profile which matches the
bit depth and chroma subsampling of the input.
The wrapper also has some specific options:
- cpu-used
- Set the quality/encoding speed tradeoff. Valid range is from 0 to 8,
higher numbers indicating greater speed and lower quality. The default
value is 1, which will be slow and high quality.
- auto-alt-ref
- Enable use of alternate reference frames. Defaults to the internal default
of the library.
- arnr-max-frames
(frames)
- Set altref noise reduction max frame count. Default is -1.
- arnr-strength
(strength)
- Set altref noise reduction filter strength. Range is -1 to 6. Default is
-1.
- aq-mode
(aq-mode)
- Set adaptive quantization mode. Possible values:
- tune
(tune)
- Set the distortion metric the encoder is tuned with. Default is
"psnr".
- lag-in-frames
- Set the maximum number of frames which the encoder may keep in flight at
any one time for lookahead purposes. Defaults to the internal default of
the library.
- error-resilience
- Enable error resilience features:
- default
- Improve resilience against losses of whole frames.
- crf
- Set the quality/size tradeoff for constant-quality (no bitrate target) and
constrained-quality (with maximum bitrate target) modes. Valid range is 0
to 63, higher numbers indicating lower quality and smaller output size.
Only used if set; by default only the bitrate target is used.
- static-thresh
- Set a change threshold on blocks below which they will be skipped by the
encoder. Defined in arbitrary units as a nonnegative integer, defaulting
to zero (no blocks are skipped).
- drop-threshold
- Set a threshold for dropping frames when close to rate control bounds.
Defined as a percentage of the target buffer - when the rate control
buffer falls below this percentage, frames will be dropped until it has
refilled above the threshold. Defaults to zero (no frames are
dropped).
- denoise-noise-level
(level)
- Amount of noise to be removed for grain synthesis. Grain synthesis is
disabled if this option is not set or set to 0.
- denoise-block-size
(pixels)
- Block size used for denoising for grain synthesis. If not set, AV1 codec
uses the default value of 32.
- undershoot-pct
(pct)
- Set datarate undershoot (min) percentage of the target bitrate. Range is
-1 to 100. Default is -1.
- overshoot-pct
(pct)
- Set datarate overshoot (max) percentage of the target bitrate. Range is -1
to 1000. Default is -1.
- minsection-pct
(pct)
- Minimum percentage variation of the GOP bitrate from the target bitrate.
If minsection-pct is not set, the libaomenc wrapper computes it as
follows: "(minrate * 100 / bitrate)".
Range is -1 to 100. Default is -1 (unset).
- maxsection-pct
(pct)
- Maximum percentage variation of the GOP bitrate from the target bitrate.
If maxsection-pct is not set, the libaomenc wrapper computes it as
follows: "(maxrate * 100 / bitrate)".
Range is -1 to 5000. Default is -1 (unset).
- frame-parallel
(boolean)
- Enable frame parallel decodability features. Default is true.
- tiles
- Set the number of tiles to encode the input video with, as columns x rows.
Larger numbers allow greater parallelism in both encoding and decoding,
but may decrease coding efficiency. Defaults to the minimum number of
tiles required by the size of the input video (this is 1x1 (that is, a
single tile) for sizes up to and including 4K).
- tile-columns
tile-rows
- Set the number of tiles as log2 of the number of tile rows and columns.
Provided for compatibility with libvpx/VP9.
- row-mt (Requires libaom
>= 1.0.0-759-g90a15f4f2)
- Enable row based multi-threading. Disabled by default.
- enable-cdef
(boolean)
- Enable Constrained Directional Enhancement Filter. The libaom-av1 encoder
enables CDEF by default.
- enable-restoration
(boolean)
- Enable Loop Restoration Filter. Default is true for libaom-av1.
- enable-global-motion
(boolean)
- Enable the use of global motion for block prediction. Default is
true.
- enable-intrabc
(boolean)
- Enable block copy mode for intra block prediction. This mode is useful for
screen content. Default is true.
Kvazaar H.265/HEVC encoder.
Requires the presence of the libkvazaar headers and library during
configuration. You need to explicitly configure the build with
--enable-libkvazaar.
Options
- b
- Set target video bitrate in bit/s and enable rate control.
- kvazaar-params
- Set kvazaar parameters as a list of name=value pairs
separated by commas (,). See kvazaar documentation for a list of
options.
Cisco libopenh264 H.264/MPEG-4 AVC encoder wrapper.
This encoder requires the presence of the libopenh264 headers and
library during configuration. You need to explicitly configure the build
with "--enable-libopenh264". The library
is detected using pkg-config.
For more information about the library see
<http://www.openh264.org>.
Options
The following FFmpeg global options affect the configurations of
the libopenh264 encoder.
- b
- Set the bitrate (as a number of bits per second).
- g
- Set the GOP size.
- maxrate
- Set the max bitrate (as a number of bits per second).
- flags
+global_header
- Set global header in the bitstream.
- slices
- Set the number of slices, used in parallelized encoding. Default value is
0. This is only used when slice_mode is set to fixed.
- slice_mode
- Set slice mode. Can assume one of the following possible values:
- fixed
- a fixed number of slices
- rowmb
- one slice per row of macroblocks
- auto
- automatic number of slices according to number of threads
- dyn
- dynamic slicing
- loopfilter
- Enable loop filter, if set to 1 (automatically enabled). To disable set a
value of 0.
- profile
- Set profile restrictions. If set to the value of main enable CABAC
(set the
"SEncParamExt.iEntropyCodingModeFlag"
flag to 1).
- max_nal_size
- Set maximum NAL size in bytes.
- allow_skip_frames
- Allow skipping frames to hit the target bitrate if set to 1.
libtheora Theora encoder wrapper.
Requires the presence of the libtheora headers and library during
configuration. You need to explicitly configure the build with
"--enable-libtheora".
For more information about the libtheora project see
<http://www.theora.org/>.
Options
The following global options are mapped to internal libtheora
options which affect the quality and the bitrate of the encoded stream.
- b
- Set the video bitrate in bit/s for CBR (Constant Bit Rate) mode. In case
VBR (Variable Bit Rate) mode is enabled this option is ignored.
- flags
- Used to enable constant quality mode (VBR) encoding through the
qscale flag, and to enable the
"pass1" and
"pass2" modes.
- g
- Set the GOP size.
- global_quality
- Set the global quality as an integer in lambda units.
Only relevant when VBR mode is enabled with
"flags +qscale". The value is
converted to QP units by dividing it by
"FF_QP2LAMBDA", clipped in the [0 -
10] range, and then multiplied by 6.3 to get a value in the native
libtheora range [0-63]. A higher value corresponds to a higher
quality.
- q
- Enable VBR mode when set to a non-negative value, and set constant quality
value as a double floating point value in QP units.
The value is clipped in the [0-10] range, and then multiplied
by 6.3 to get a value in the native libtheora range [0-63].
This option is valid only using the ffmpeg command-line
tool. For library interface users, use global_quality.
Examples
VP8/VP9 format supported through libvpx.
Requires the presence of the libvpx headers and library during
configuration. You need to explicitly configure the build with
"--enable-libvpx".
Options
The following options are supported by the libvpx wrapper. The
vpxenc-equivalent options or values are listed in parentheses for
easy migration.
To reduce the duplication of documentation, only the private
options and some others requiring special attention are documented here. For
the documentation of the undocumented generic options, see the Codec
Options chapter.
To get more documentation of the libvpx options, invoke the
command ffmpeg -h encoder=libvpx, ffmpeg -h encoder=libvpx-vp9
or vpxenc --help. Further information is available in the libvpx API
documentation.
- b
(target-bitrate)
- Set bitrate in bits/s. Note that FFmpeg's b option is expressed in
bits/s, while vpxenc's target-bitrate is in kilobits/s.
- g
(kf-max-dist)
- keyint_min
(kf-min-dist)
- qmin
(min-q)
- qmax
(max-q)
- bufsize
(buf-sz, buf-optimal-sz)
- Set ratecontrol buffer size (in bits). Note vpxenc's options are
specified in milliseconds, the libvpx wrapper converts this value as
follows: "buf-sz = bufsize * 1000 /
bitrate", "buf-optimal-sz = bufsize *
1000 / bitrate * 5 / 6".
- rc_init_occupancy
(buf-initial-sz)
- Set number of bits which should be loaded into the rc buffer before
decoding starts. Note vpxenc's option is specified in milliseconds,
the libvpx wrapper converts this value as follows:
"rc_init_occupancy * 1000 /
bitrate".
- undershoot-pct
- Set datarate undershoot (min) percentage of the target bitrate.
- overshoot-pct
- Set datarate overshoot (max) percentage of the target bitrate.
- skip_threshold
(drop-frame)
- qcomp
(bias-pct)
- maxrate
(maxsection-pct)
- Set GOP max bitrate in bits/s. Note vpxenc's option is specified as
a percentage of the target bitrate, the libvpx wrapper converts this value
as follows: "(maxrate * 100 /
bitrate)".
- minrate
(minsection-pct)
- Set GOP min bitrate in bits/s. Note vpxenc's option is specified as
a percentage of the target bitrate, the libvpx wrapper converts this value
as follows: "(minrate * 100 /
bitrate)".
- minrate, maxrate,
b end-usage=cbr
- "(minrate == maxrate == bitrate)".
- crf
(end-usage=cq, cq-level)
- tune
(tune)
- quality, deadline
(deadline)
- best
- Use best quality deadline. Poorly named and quite slow, this option should
be avoided as it may give worse quality output than good.
- good
- Use good quality deadline. This is a good trade-off between speed and
quality when used with the cpu-used option.
- realtime
- Use realtime quality deadline.
- speed, cpu-used
(cpu-used)
- Set quality/speed ratio modifier. Higher values speed up the encode at the
cost of quality.
- nr
(noise-sensitivity)
- static-thresh
- Set a change threshold on blocks below which they will be skipped by the
encoder.
- slices
(token-parts)
- Note that FFmpeg's slices option gives the total number of
partitions, while vpxenc's token-parts is given as
"log2(partitions)".
- max-intra-rate
- Set maximum I-frame bitrate as a percentage of the target bitrate. A value
of 0 means unlimited.
- force_key_frames
- "VPX_EFLAG_FORCE_KF"
- Alternate
reference frame related
- error-resilient
- Enable error resiliency features.
- sharpness
integer
- Increase sharpness at the expense of lower PSNR. The valid range is [0,
7].
- ts-parameters
- Sets the temporal scalability configuration using a :-separated list of
key=value pairs. For example, to specify temporal scalability parameters
with "ffmpeg":
ffmpeg -i INPUT -c:v libvpx -ts-parameters ts_number_layers=3:\
ts_target_bitrate=250,500,1000:ts_rate_decimator=4,2,1:\
ts_periodicity=4:ts_layer_id=0,2,1,2:ts_layering_mode=3 OUTPUT
Below is a brief explanation of each of the parameters, please
refer to "struct vpx_codec_enc_cfg" in
"vpx/vpx_encoder.h" for more
details.
- ts_number_layers
- Number of temporal coding layers.
- ts_target_bitrate
- Target bitrate for each temporal layer (in kbps). (bitrate should be
inclusive of the lower temporal layer).
- ts_rate_decimator
- Frame rate decimation factor for each temporal layer.
- ts_periodicity
- Length of the sequence defining frame temporal layer membership.
- ts_layer_id
- Template defining the membership of frames to temporal layers.
- ts_layering_mode
- (optional) Selecting the temporal structure from a set of pre-defined
temporal layering modes. Currently supports the following options.
- 0
- No temporal layering flags are provided internally, relies on flags being
passed in using "metadata" field in
"AVFrame" with following keys.
- vp8-flags
- Sets the flags passed into the encoder to indicate the referencing scheme
for the current frame. Refer to function
"vpx_codec_encode" in
"vpx/vpx_encoder.h" for more
details.
- temporal_id
- Explicitly sets the temporal id of the current frame to encode.
- 2
- Two temporal layers. 0-1...
- 3
- Three temporal layers. 0-2-1-2...; with single reference frame.
- 4
- Same as option "3", except there is a dependency between the two
temporal layer 2 frames within the temporal period.
- VP9-specific
options
- lossless
- Enable lossless mode.
- tile-columns
- Set number of tile columns to use. Note this is given as
"log2(tile_columns)". For example, 8
tile columns would be requested by setting the tile-columns option
to 3.
- tile-rows
- Set number of tile rows to use. Note this is given as
"log2(tile_rows)". For example, 4 tile
rows would be requested by setting the tile-rows option to 2.
- frame-parallel
- Enable frame parallel decodability features.
- aq-mode
- Set adaptive quantization mode (0: off (default), 1: variance 2:
complexity, 3: cyclic refresh, 4: equator360).
- colorspace
color-space
- Set input color space. The VP9 bitstream supports signaling the following
colorspaces:
- row-mt
boolean
- Enable row based multi-threading.
- tune-content
- Set content type: default (0), screen (1), film (2).
- corpus-complexity
- Corpus VBR mode is a variant of standard VBR where the complexity
distribution midpoint is passed in rather than calculated for a specific
clip or chunk.
The valid range is [0, 10000]. 0 (default) uses standard
VBR.
- enable-tpl
boolean
- Enable temporal dependency model.
For more information about libvpx see:
<http://www.webmproject.org/>
libwebp WebP Image encoder wrapper
libwebp is Google's official encoder for WebP images. It can
encode in either lossy or lossless mode. Lossy images are essentially a
wrapper around a VP8 frame. Lossless images are a separate codec developed
by Google.
Pixel Format
Currently, libwebp only supports YUV420 for lossy and RGB for
lossless due to limitations of the format and libwebp. Alpha is supported
for either mode. Because of API limitations, if RGB is passed in when
encoding lossy or YUV is passed in for encoding lossless, the pixel format
will automatically be converted using functions from libwebp. This is not
ideal and is done only for convenience.
Options
- -lossless
boolean
- Enables/Disables use of lossless mode. Default is 0.
- -compression_level
integer
- For lossy, this is a quality/speed tradeoff. Higher values give better
quality for a given size at the cost of increased encoding time. For
lossless, this is a size/speed tradeoff. Higher values give smaller size
at the cost of increased encoding time. More specifically, it controls the
number of extra algorithms and compression tools used, and varies the
combination of these tools. This maps to the method option in
libwebp. The valid range is 0 to 6. Default is 4.
- -qscale
float
- For lossy encoding, this controls image quality, 0 to 100. For lossless
encoding, this controls the effort and time spent at compressing more. The
default value is 75. Note that for usage via libavcodec, this option is
called global_quality and must be multiplied by
FF_QP2LAMBDA.
- -preset
type
- Configuration preset. This does some automatic settings based on the
general type of the image.
- none
- Do not use a preset.
- default
- Use the encoder default.
- picture
- Digital picture, like portrait, inner shot
- photo
- Outdoor photograph, with natural lighting
- drawing
- Hand or line drawing, with high-contrast details
- icon
- Small-sized colorful images
- text
- Text-like
x264 H.264/MPEG-4 AVC encoder wrapper.
This encoder requires the presence of the libx264 headers and
library during configuration. You need to explicitly configure the build
with "--enable-libx264".
libx264 supports an impressive number of features, including 8x8
and 4x4 adaptive spatial transform, adaptive B-frame placement, CAVLC/CABAC
entropy coding, interlacing (MBAFF), lossless mode, psy optimizations for
detail retention (adaptive quantization, psy-RD, psy-trellis).
Many libx264 encoder options are mapped to FFmpeg global codec
options, while unique encoder options are provided through private options.
Additionally the x264opts and x264-params private options
allows one to pass a list of key=value tuples as accepted by the libx264
"x264_param_parse" function.
The x264 project website is at
<http://www.videolan.org/developers/x264.html>.
The libx264rgb encoder is the same as libx264, except it accepts
packed RGB pixel formats as input instead of YUV.
Supported Pixel Formats
x264 supports 8- to 10-bit color spaces. The exact bit depth is
controlled at x264's configure time. FFmpeg only supports one bit depth in
one particular build. In other words, it is not possible to build one FFmpeg
with multiple versions of x264 with different bit depths.
Options
The following options are supported by the libx264 wrapper. The
x264-equivalent options or values are listed in parentheses for easy
migration.
To reduce the duplication of documentation, only the private
options and some others requiring special attention are documented here. For
the documentation of the undocumented generic options, see the Codec
Options chapter.
To get a more accurate and extensive documentation of the libx264
options, invoke the command x264 --fullhelp or consult the libx264
documentation.
- b
(bitrate)
- Set bitrate in bits/s. Note that FFmpeg's b option is expressed in
bits/s, while x264's bitrate is in kilobits/s.
- bf
(bframes)
- g
(keyint)
- qmin
(qpmin)
- Minimum quantizer scale.
- qmax
(qpmax)
- Maximum quantizer scale.
- qdiff
(qpstep)
- Maximum difference between quantizer scales.
- qblur
(qblur)
- Quantizer curve blur
- qcomp
(qcomp)
- Quantizer curve compression factor
- refs
(ref)
- Number of reference frames each P-frame can use. The range is from
0-16.
- sc_threshold
(scenecut)
- Sets the threshold for the scene change detection.
- trellis
(trellis)
- Performs Trellis quantization to increase efficiency. Enabled by
default.
- nr
(nr)
- me_range
(merange)
- Maximum range of the motion search in pixels.
- me_method
(me)
- Set motion estimation method. Possible values in the decreasing order of
speed:
- forced-idr
- Normally, when forcing a I-frame type, the encoder can select any type of
I-frame. This option forces it to choose an IDR-frame.
- subq
(subme)
- Sub-pixel motion estimation method.
- b_strategy
(b-adapt)
- Adaptive B-frame placement decision algorithm. Use only on
first-pass.
- keyint_min
(min-keyint)
- Minimum GOP size.
- coder
- Set entropy encoder. Possible values:
- ac
- Enable CABAC.
- vlc
- Enable CAVLC and disable CABAC. It generates the same effect as
x264's --no-cabac option.
- cmp
- Set full pixel motion estimation comparison algorithm. Possible
values:
- chroma
- Enable chroma in motion estimation.
- sad
- Ignore chroma in motion estimation. It generates the same effect as
x264's --no-chroma-me option.
- threads
(threads)
- Number of encoding threads.
- thread_type
- Set multithreading technique. Possible values:
- slice
- Slice-based multithreading. It generates the same effect as x264's
--sliced-threads option.
- frame
- Frame-based multithreading.
- flags
- Set encoding flags. It can be used to disable closed GOP and enable open
GOP by setting it to "-cgop". The result
is similar to the behavior of x264's --open-gop option.
- rc_init_occupancy
(vbv-init)
- preset
(preset)
- Set the encoding preset.
- tune
(tune)
- Set tuning of the encoding params.
- profile
(profile)
- Set profile restrictions.
- fastfirstpass
- Enable fast settings when encoding first pass, when set to 1. When set to
0, it has the same effect of x264's --slow-firstpass
option.
- crf
(crf)
- Set the quality for constant quality mode.
- crf_max
(crf-max)
- In CRF mode, prevents VBV from lowering quality beyond this point.
- qp
(qp)
- Set constant quantization rate control method parameter.
- aq-mode
(aq-mode)
- Set AQ method. Possible values:
- aq-strength
(aq-strength)
- Set AQ strength, reduce blocking and blurring in flat and textured
areas.
- psy
- Use psychovisual optimizations when set to 1. When set to 0, it has the
same effect as x264's --no-psy option.
- psy-rd
(psy-rd)
- Set strength of psychovisual optimization, in
psy-rd:psy-trellis format.
- rc-lookahead
(rc-lookahead)
- Set number of frames to look ahead for frametype and ratecontrol.
- weightb
- Enable weighted prediction for B-frames when set to 1. When set to 0, it
has the same effect as x264's --no-weightb option.
- weightp
(weightp)
- Set weighted prediction method for P-frames. Possible values:
- ssim
(ssim)
- Enable calculation and printing SSIM stats after the encoding.
- intra-refresh
(intra-refresh)
- Enable the use of Periodic Intra Refresh instead of IDR frames when set to
1.
- avcintra-class
(class)
- Configure the encoder to generate AVC-Intra. Valid values are 50,100 and
200
- bluray-compat
(bluray-compat)
- Configure the encoder to be compatible with the bluray standard. It is a
shorthand for setting "bluray-compat=1 force-cfr=1".
- b-bias
(b-bias)
- Set the influence on how often B-frames are used.
- b-pyramid
(b-pyramid)
- Set method for keeping of some B-frames as references. Possible
values:
- mixed-refs
- Enable the use of one reference per partition, as opposed to one reference
per macroblock when set to 1. When set to 0, it has the same effect as
x264's --no-mixed-refs option.
- 8x8dct
- Enable adaptive spatial transform (high profile 8x8 transform) when set to
1. When set to 0, it has the same effect as x264's
--no-8x8dct option.
- fast-pskip
- Enable early SKIP detection on P-frames when set to 1. When set to 0, it
has the same effect as x264's --no-fast-pskip option.
- aud
(aud)
- Enable use of access unit delimiters when set to 1.
- mbtree
- Enable use macroblock tree ratecontrol when set to 1. When set to 0, it
has the same effect as x264's --no-mbtree option.
- deblock
(deblock)
- Set loop filter parameters, in alpha:beta form.
- cplxblur
(cplxblur)
- Set fluctuations reduction in QP (before curve compression).
- partitions
(partitions)
- Set partitions to consider as a comma-separated list of. Possible values
in the list:
- p8x8
- 8x8 P-frame partition.
- p4x4
- 4x4 P-frame partition.
- b8x8
- 4x4 B-frame partition.
- i8x8
- 8x8 I-frame partition.
- i4x4
- 4x4 I-frame partition. (Enabling p4x4 requires p8x8 to be
enabled. Enabling i8x8 requires adaptive spatial transform
(8x8dct option) to be enabled.)
- none
(none)
- Do not consider any partitions.
- all
(all)
- Consider every partition.
- direct-pred
(direct)
- Set direct MV prediction mode. Possible values:
- slice-max-size
(slice-max-size)
- Set the limit of the size of each slice in bytes. If not specified but RTP
payload size (ps) is specified, that is used.
- stats
(stats)
- Set the file name for multi-pass stats.
- nal-hrd
(nal-hrd)
- Set signal HRD information (requires vbv-bufsize to be set).
Possible values:
- x264opts
(N.A.)
- Set any x264 option, see x264 --fullhelp for a list.
Argument is a list of key=value couples
separated by ":". In filter and psy-rd options
that use ":" as a separator themselves, use ","
instead. They accept it as well since long ago but this is kept
undocumented for some reason.
For example to specify libx264 encoding options with
ffmpeg:
ffmpeg -i foo.mpg -c:v libx264 -x264opts keyint=123:min-keyint=20 -an out.mkv
- a53cc
boolean
- Import closed captions (which must be ATSC compatible format) into output.
Only the mpeg2 and h264 decoders provide these. Default is 1 (on).
- x264-params
(N.A.)
- Override the x264 configuration using a :-separated list of key=value
parameters.
This option is functionally the same as the x264opts,
but is duplicated for compatibility with the Libav fork.
For example to specify libx264 encoding options with
ffmpeg:
ffmpeg -i INPUT -c:v libx264 -x264-params level=30:bframes=0:weightp=0:\
cabac=0:ref=1:vbv-maxrate=768:vbv-bufsize=2000:analyse=all:me=umh:\
no-fast-pskip=1:subq=6:8x8dct=0:trellis=0 OUTPUT
Encoding ffpresets for common usages are provided so they can be
used with the general presets system (e.g. passing the pre
option).
x265 H.265/HEVC encoder wrapper.
This encoder requires the presence of the libx265 headers and
library during configuration. You need to explicitly configure the build
with --enable-libx265.
Options
- b
- Sets target video bitrate.
- bf
- g
- Set the GOP size.
- keyint_min
- Minimum GOP size.
- refs
- Number of reference frames each P-frame can use. The range is from
1-16.
- preset
- Set the x265 preset.
- tune
- Set the x265 tune parameter.
- profile
- Set profile restrictions.
- crf
- Set the quality for constant quality mode.
- qp
- Set constant quantization rate control method parameter.
- qmin
- Minimum quantizer scale.
- qmax
- Maximum quantizer scale.
- qdiff
- Maximum difference between quantizer scales.
- qblur
- Quantizer curve blur
- qcomp
- Quantizer curve compression factor
- i_qfactor
- b_qfactor
- forced-idr
- Normally, when forcing a I-frame type, the encoder can select any type of
I-frame. This option forces it to choose an IDR-frame.
- x265-params
- Set x265 options using a list of key=value couples separated
by ":". See x265 --help for a list of options.
For example to specify libx265 encoding options with
-x265-params:
ffmpeg -i input -c:v libx265 -x265-params crf=26:psy-rd=1 output.mp4
xavs2 AVS2-P2/IEEE1857.4 encoder wrapper.
This encoder requires the presence of the libxavs2 headers and
library during configuration. You need to explicitly configure the build
with --enable-libxavs2.
The following standard libavcodec options are used:
- b / bit_rate
- g / gop_size
- bf / max_b_frames
The encoder also has its own specific options:
Options
- lcu_row_threads
- Set the number of parallel threads for rows from 1 to 8 (default 5).
- initial_qp
- Set the xavs2 quantization parameter from 1 to 63 (default 34). This is
used to set the initial qp for the first frame.
- qp
- Set the xavs2 quantization parameter from 1 to 63 (default 34). This is
used to set the qp value under constant-QP mode.
- max_qp
- Set the max qp for rate control from 1 to 63 (default 55).
- min_qp
- Set the min qp for rate control from 1 to 63 (default 20).
- speed_level
- Set the Speed level from 0 to 9 (default 0). Higher is better but
slower.
- log_level
- Set the log level from -1 to 3 (default 0). -1: none, 0: error, 1:
warning, 2: info, 3: debug.
- xavs2-params
- Set xavs2 options using a list of key=value couples
separated by ":".
For example to specify libxavs2 encoding options with
-xavs2-params:
ffmpeg -i input -c:v libxavs2 -xavs2-params RdoqLevel=0 output.avs2
Xvid MPEG-4 Part 2 encoder wrapper.
This encoder requires the presence of the libxvidcore headers and
library during configuration. You need to explicitly configure the build
with "--enable-libxvid --enable-gpl".
The native "mpeg4" encoder
supports the MPEG-4 Part 2 format, so users can encode to this format
without this library.
Options
The following options are supported by the libxvid wrapper. Some
of the following options are listed but are not documented, and correspond
to shared codec options. See the Codec Options chapter for
their documentation. The other shared options which are not listed have no
effect for the libxvid encoder.
- b
- g
- qmin
- qmax
- mpeg_quant
- threads
- bf
- b_qfactor
- b_qoffset
- flags
- Set specific encoding flags. Possible values:
- mv4
- Use four motion vector by macroblock.
- aic
- Enable high quality AC prediction.
- gray
- Only encode grayscale.
- gmc
- Enable the use of global motion compensation (GMC).
- qpel
- Enable quarter-pixel motion compensation.
- cgop
- Enable closed GOP.
- Place global headers in extradata instead of every keyframe.
- trellis
- me_method
- Set motion estimation method. Possible values in decreasing order of speed
and increasing order of quality:
- zero
- Use no motion estimation (default).
- phods
- x1
- log
- Enable advanced diamond zonal search for 16x16 blocks and half-pixel
refinement for 16x16 blocks. x1 and log are aliases for
phods.
- epzs
- Enable all of the things described above, plus advanced diamond zonal
search for 8x8 blocks, half-pixel refinement for 8x8 blocks, and motion
estimation on chroma planes.
- full
- Enable all of the things described above, plus extended 16x16 and 8x8
blocks search.
- mbd
- Set macroblock decision algorithm. Possible values in the increasing order
of quality:
- simple
- Use macroblock comparing function algorithm (default).
- bits
- Enable rate distortion-based half pixel and quarter pixel refinement for
16x16 blocks.
- rd
- Enable all of the things described above, plus rate distortion-based half
pixel and quarter pixel refinement for 8x8 blocks, and rate
distortion-based search using square pattern.
- lumi_aq
- Enable lumi masking adaptive quantization when set to 1. Default is 0
(disabled).
- variance_aq
- Enable variance adaptive quantization when set to 1. Default is 0
(disabled).
When combined with lumi_aq, the resulting quality will
not be better than any of the two specified individually. In other
words, the resulting quality will be the worse one of the two
effects.
- ssim
- Set structural similarity (SSIM) displaying method. Possible values:
- off
- Disable displaying of SSIM information.
- avg
- Output average SSIM at the end of encoding to stdout. The format of
showing the average SSIM is:
Average SSIM: %f
For users who are not familiar with C,
%f means a float number, or a decimal (e.g.
0.939232).
- frame
- Output both per-frame SSIM data during encoding and average SSIM at the
end of encoding to stdout. The format of per-frame information is:
SSIM: avg: %1.3f min: %1.3f max: %1.3f
For users who are not familiar with C,
%1.3f means a float number rounded to 3 digits
after the dot (e.g. 0.932).
- ssim_acc
- Set SSIM accuracy. Valid options are integers within the range of 0-4,
while 0 gives the most accurate result and 4 computes the fastest.
This provides wrappers to encoders (both audio and video) in the
MediaFoundation framework. It can access both SW and HW encoders. Video
encoders can take input in either of nv12 or yuv420p form (some encoders
support both, some support only either - in practice, nv12 is the safer
choice, especially among HW encoders).
MPEG-2 video encoder.
Options
- profile
integer
- Select the mpeg2 profile to encode:
- seq_disp_ext
integer
- Specifies if the encoder should write a sequence_display_extension to the
output.
- -1
- auto
- Decide automatically to write it or not (this is the default) by checking
if the data to be written is different from the default or unspecified
values.
- 0
- never
- Never write it.
- 1
- always
- Always write it.
- video_format
integer
- Specifies the video_format written into the sequence display extension
indicating the source of the video pictures. The default is
unspecified, can be component, pal, ntsc,
secam or mac. For maximum compatibility, use
component.
- a53cc
boolean
- Import closed captions (which must be ATSC compatible format) into output.
Default is 1 (on).
PNG image encoder.
Private options
- dpi
integer
- Set physical density of pixels, in dots per inch, unset by default
- dpm
integer
- Set physical density of pixels, in dots per meter, unset by default
Apple ProRes encoder.
FFmpeg contains 2 ProRes encoders, the prores-aw and prores-ks
encoder. The used encoder can be chosen with the
"-vcodec" option.
Private Options for prores-ks
- profile
integer
- Select the ProRes profile to encode
- quant_mat
integer
- Select quantization matrix.
If set to auto, the matrix matching the profile will be
picked. If not set, the matrix providing the highest quality,
default, will be picked.
- bits_per_mb
integer
- How many bits to allot for coding one macroblock. Different profiles use
between 200 and 2400 bits per macroblock, the maximum is 8000.
- mbs_per_slice
integer
- Number of macroblocks in each slice (1-8); the default value (8) should be
good in almost all situations.
- vendor
string
- Override the 4-byte vendor ID. A custom vendor ID like apl0 would
claim the stream was produced by the Apple encoder.
- alpha_bits
integer
- Specify number of bits for alpha component. Possible values are 0,
8 and 16. Use 0 to disable alpha plane coding.
Speed considerations
In the default mode of operation the encoder has to honor frame
constraints (i.e. not produce frames with size bigger than requested) while
still making output picture as good as possible. A frame containing a lot of
small details is harder to compress and the encoder would spend more time
searching for appropriate quantizers for each slice.
Setting a higher bits_per_mb limit will improve the
speed.
For the fastest encoding speed set the qscale parameter (4
is the recommended value) and do not set a size constraint.
QSV encoders
The family of Intel QuickSync Video encoders (MPEG-2, H.264, HEVC,
JPEG/MJPEG and VP9)
The ratecontrol method is selected as follows:
- •
- When global_quality is specified, a quality-based mode is used.
Specifically this means either
- CQP - constant quantizer scale, when the qscale codec flag
is also set (the -qscale ffmpeg option).
- LA_ICQ - intelligent constant quality with lookahead, when the
look_ahead option is also set.
- ICQ -- intelligent constant quality otherwise.
- •
- Otherwise, a bitrate-based mode is used. For all of those, you should
specify at least the desired average bitrate with the b
option.
- LA - VBR with lookahead, when the look_ahead option is
specified.
- VCM - video conferencing mode, when the vcm option is
set.
- CBR - constant bitrate, when maxrate is specified and equal
to the average bitrate.
- VBR - variable bitrate, when maxrate is specified, but is
higher than the average bitrate.
- AVBR - average VBR mode, when maxrate is not specified. This
mode is further configured by the avbr_accuracy and
avbr_convergence options.
Note that depending on your system, a different mode than the one
you specified may be selected by the encoder. Set the verbosity level to
verbose or higher to see the actual settings used by the QSV
runtime.
Additional libavcodec global options are mapped to MSDK options as
follows:
- g/gop_size -> GopPicSize
- bf/max_b_frames+1 -> GopRefDist
- rc_init_occupancy/rc_initial_buffer_occupancy ->
InitialDelayInKB
- slices -> NumSlice
- refs -> NumRefFrame
- b_strategy/b_frame_strategy -> BRefType
- cgop/CLOSED_GOP codec flag -> GopOptFlag
- For the CQP mode, the i_qfactor/i_qoffset and
b_qfactor/b_qoffset set the difference between QPP and
QPI, and QPP and QPB respectively.
- Setting the coder option to the value vlc will make the
H.264 encoder use CAVLC instead of CABAC.
VAAPI encoders
Wrappers for hardware encoders accessible via VAAPI.
These encoders only accept input in VAAPI hardware surfaces. If
you have input in software frames, use the hwupload filter to upload
them to the GPU.
The following standard libavcodec options are used:
- g / gop_size
- bf / max_b_frames
- profile
If not set, this will be determined automatically from the
format of the input frames and the profiles supported by the driver.
- level
- b / bit_rate
- maxrate / rc_max_rate
- bufsize / rc_buffer_size
- rc_init_occupancy / rc_initial_buffer_occupancy
- compression_level
Speed / quality tradeoff: higher values are faster / worse
quality.
- q / global_quality
Size / quality tradeoff: higher values are smaller / worse
quality.
- qmin
- qmax
- i_qfactor / i_quant_factor
- i_qoffset / i_quant_offset
- b_qfactor / b_quant_factor
- b_qoffset / b_quant_offset
- slices
All encoders support the following options:
- low_power
- Some drivers/platforms offer a second encoder for some codecs intended to
use less power than the default encoder; setting this option will attempt
to use that encoder. Note that it may support a reduced feature set, so
some other options may not be available in this mode.
- idr_interval
- Set the number of normal intra frames between full-refresh (IDR) frames in
open-GOP mode. The intra frames are still IRAPs, but will not include
global headers and may have non-decodable leading pictures.
- b_depth
- Set the B-frame reference depth. When set to one (the default), all
B-frames will refer only to P- or I-frames. When set to greater values
multiple layers of B-frames will be present, frames in each layer only
referring to frames in higher layers.
- rc_mode
- Set the rate control mode to use. A given driver may only support a subset
of modes.
Possible modes:
- auto
- Choose the mode automatically based on driver support and the other
options. This is the default.
- CQP
- Constant-quality.
- CBR
- Constant-bitrate.
- VBR
- Variable-bitrate.
- ICQ
- Intelligent constant-quality.
- QVBR
- Quality-defined variable-bitrate.
- AVBR
- Average variable bitrate.
Each encoder also has its own specific options:
- h264_vaapi
- profile sets the value of profile_idc and the
constraint_set*_flags. level sets the value of
level_idc.
- coder
- Set entropy encoder (default is cabac). Possible values:
- aud
- Include access unit delimiters in the stream (not included by
default).
- sei
- Set SEI message types to include. Some combination of the following
values:
- identifier
- Include a user_data_unregistered message containing information
about the encoder.
- timing
- Include picture timing parameters (buffering_period and
pic_timing messages).
- recovery_point
- Include recovery points where appropriate (recovery_point
messages).
- hevc_vaapi
- profile and level set the values of
general_profile_idc and general_level_idc respectively.
- aud
- Include access unit delimiters in the stream (not included by
default).
- tier
- Set general_tier_flag. This may affect the level chosen for the
stream if it is not explicitly specified.
- sei
- Set SEI message types to include. Some combination of the following
values:
- hdr
- Include HDR metadata if the input frames have it
(mastering_display_colour_volume and content_light_level
messages).
- mjpeg_vaapi
- Only baseline DCT encoding is supported. The encoder always uses the
standard quantisation and huffman tables - global_quality scales
the standard quantisation table (range 1-100).
For YUV, 4:2:0, 4:2:2 and 4:4:4 subsampling modes are
supported. RGB is also supported, and will create an RGB JPEG.
- jfif
- Include JFIF header in each frame (not included by default).
- huffman
- Include standard huffman tables (on by default). Turning this off will
save a few hundred bytes in each output frame, but may lose compatibility
with some JPEG decoders which don't fully handle MJPEG.
- mpeg2_vaapi
- profile and level set the value of
profile_and_level_indication.
- vp8_vaapi
- B-frames are not supported.
global_quality sets the q_idx used for non-key
frames (range 0-127).
- vp9_vaapi
- global_quality sets the q_idx used for P-frames (range
0-255).
B-frames are supported, but the output stream is always in encode
order rather than display order. If B-frames are enabled, it may be
necessary to use the vp9_raw_reorder bitstream filter to modify the
output stream to display frames in the correct order.
Only normal frames are produced - the vp9_superframe
bitstream filter may be required to produce a stream usable with all
decoders.
SMPTE VC-2 (previously BBC Dirac Pro). This codec was primarily
aimed at professional broadcasting but since it supports yuv420, yuv422 and
yuv444 at 8 (limited range or full range), 10 or 12 bits, this makes it
suitable for other tasks which require low overhead and low compression
(like screen recording).
Options
- b
- Sets target video bitrate. Usually that's around 1:6 of the uncompressed
video bitrate (e.g. for 1920x1080 50fps yuv422p10 that's around 400Mbps).
Higher values (close to the uncompressed bitrate) turn on lossless
compression mode.
- field_order
- Enables field coding when set (e.g. to tt - top field first) for
interlaced inputs. Should increase compression with interlaced content as
it splits the fields and encodes each separately.
- wavelet_depth
- Sets the total amount of wavelet transforms to apply, between 1 and 5
(default). Lower values reduce compression and quality. Less capable
decoders may not be able to handle values of wavelet_depth over
3.
- wavelet_type
- Sets the transform type. Currently only 5_3 (LeGall) and 9_7
(Deslauriers-Dubuc) are implemented, with 9_7 being the one with better
compression and thus is the default.
- slice_width
- slice_height
- Sets the slice size for each slice. Larger values result in better
compression. For compatibility with other more limited decoders use
slice_width of 32 and slice_height of 8.
- tolerance
- Sets the undershoot tolerance of the rate control system in percent. This
is to prevent an expensive search from being run.
- qm
- Sets the quantization matrix preset to use by default or when
wavelet_depth is set to 5
- default Uses the default quantization matrix from the
specifications, extended with values for the fifth level. This provides a
good balance between keeping detail and omitting artifacts.
- flat Use a completely zeroed out quantization matrix. This
increases PSNR but might reduce perception. Use in bogus benchmarks.
- color Reduces detail but attempts to preserve color at extremely
low bitrates.