DOKK / manpages / debian 13 / libopus-doc / opus_decoder.3.en
opus_decoder(3) Opus opus_decoder(3)

opus_decoder - Opus Decoder


- This page describes the process and functions used to decode Opus.


typedef struct OpusDecoder OpusDecoder
Opus decoder state. typedef struct OpusDREDDecoder OpusDREDDecoder
Opus DRED decoder. typedef struct OpusDRED OpusDRED
Opus DRED state.


int opus_decoder_get_size (int channels)
Gets the size of an OpusDecoder structure. OpusDecoder * opus_decoder_create (opus_int32 Fs, int channels, int *error)
Allocates and initializes a decoder state. int opus_decoder_init (OpusDecoder *st, opus_int32 Fs, int channels)
Initializes a previously allocated decoder state. int opus_decode (OpusDecoder *st, const unsigned char *data, opus_int32 len, opus_int16 *pcm, int frame_size, int decode_fec)
Decode an Opus packet. int opus_decode_float (OpusDecoder *st, const unsigned char *data, opus_int32 len, float *pcm, int frame_size, int decode_fec)
Decode an Opus packet with floating point output. int opus_decoder_ctl (OpusDecoder *st, int request,...)
Perform a CTL function on an Opus decoder. void opus_decoder_destroy (OpusDecoder *st)
Frees an OpusDecoder allocated by opus_decoder_create(). int opus_dred_decoder_get_size (void)
Gets the size of an OpusDREDDecoder structure. OpusDREDDecoder * opus_dred_decoder_create (int *error)
Allocates and initializes an OpusDREDDecoder state. int opus_dred_decoder_init (OpusDREDDecoder *dec)
Initializes an OpusDREDDecoder state. void opus_dred_decoder_destroy (OpusDREDDecoder *dec)
Frees an OpusDREDDecoder allocated by opus_dred_decoder_create(). int opus_dred_decoder_ctl (OpusDREDDecoder *dred_dec, int request,...)
Perform a CTL function on an Opus DRED decoder. int opus_dred_get_size (void)
Gets the size of an OpusDRED structure. OpusDRED * opus_dred_alloc (int *error)
Allocates and initializes a DRED state. void opus_dred_free (OpusDRED *dec)
Frees an OpusDRED allocated by opus_dred_create(). int opus_dred_parse (OpusDREDDecoder *dred_dec, OpusDRED *dred, const unsigned char *data, opus_int32 len, opus_int32 max_dred_samples, opus_int32 sampling_rate, int *dred_end, int defer_processing)
Decode an Opus DRED packet. int opus_dred_process (OpusDREDDecoder *dred_dec, const OpusDRED *src, OpusDRED *dst)
Finish decoding an Opus DRED packet. int opus_decoder_dred_decode (OpusDecoder *st, const OpusDRED *dred, opus_int32 dred_offset, opus_int16 *pcm, opus_int32 frame_size)
Decode audio from an Opus DRED packet with floating point output. int opus_decoder_dred_decode_float (OpusDecoder *st, const OpusDRED *dred, opus_int32 dred_offset, float *pcm, opus_int32 frame_size)
Decode audio from an Opus DRED packet with floating point output. int opus_packet_parse (const unsigned char *data, opus_int32 len, unsigned char *out_toc, const unsigned char *frames[48], opus_int16 size[48], int *payload_offset)
Parse an opus packet into one or more frames. int opus_packet_get_bandwidth (const unsigned char *data)
Gets the bandwidth of an Opus packet. int opus_packet_get_samples_per_frame (const unsigned char *data, opus_int32 Fs)
Gets the number of samples per frame from an Opus packet. int opus_packet_get_nb_channels (const unsigned char *data)
Gets the number of channels from an Opus packet. int opus_packet_get_nb_frames (const unsigned char packet[], opus_int32 len)
Gets the number of frames in an Opus packet. int opus_packet_get_nb_samples (const unsigned char packet[], opus_int32 len, opus_int32 Fs)
Gets the number of samples of an Opus packet. int opus_packet_has_lbrr (const unsigned char packet[], opus_int32 len)
Checks whether an Opus packet has LBRR. int opus_decoder_get_nb_samples (const OpusDecoder *dec, const unsigned char packet[], opus_int32 len)
Gets the number of samples of an Opus packet. void opus_pcm_soft_clip (float *pcm, int frame_size, int channels, float *softclip_mem)
Applies soft-clipping to bring a float signal within the [-1,1] range.

This page describes the process and functions used to decode Opus.

The decoding process also starts with creating a decoder state. This can be done with:

int          error;
OpusDecoder *dec;
dec = opus_decoder_create(Fs, channels, &error);


where

  • Fs is the sampling rate and must be 8000, 12000, 16000, 24000, or 48000
  • channels is the number of channels (1 or 2)
  • error will hold the error code in case of failure (or OPUS_OK on success)
  • the return value is a newly created decoder state to be used for decoding

While opus_decoder_create() allocates memory for the state, it's also possible to initialize pre-allocated memory:

int          size;
int          error;
OpusDecoder *dec;
size = opus_decoder_get_size(channels);
dec = malloc(size);
error = opus_decoder_init(dec, Fs, channels);


where opus_decoder_get_size() returns the required size for the decoder state. Note that future versions of this code may change the size, so no assumptions should be made about it.

The decoder state is always continuous in memory and only a shallow copy is sufficient to copy it (e.g. memcpy())

To decode a frame, opus_decode() or opus_decode_float() must be called with a packet of compressed audio data:

frame_size = opus_decode(dec, packet, len, decoded, max_size, 0);


where

  • packet is the byte array containing the compressed data
  • len is the exact number of bytes contained in the packet
  • decoded is the decoded audio data in opus_int16 (or float for opus_decode_float())
  • max_size is the max duration of the frame in samples (per channel) that can fit into the decoded_frame array

opus_decode() and opus_decode_float() return the number of samples (per channel) decoded from the packet. If that value is negative, then an error has occurred. This can occur if the packet is corrupted or if the audio buffer is too small to hold the decoded audio.

Opus is a stateful codec with overlapping blocks and as a result Opus packets are not coded independently of each other. Packets must be passed into the decoder serially and in the correct order for a correct decode. Lost packets can be replaced with loss concealment by calling the decoder with a null pointer and zero length for the missing packet.

A single codec state may only be accessed from a single thread at a time and any required locking must be performed by the caller. Separate streams must be decoded with separate decoder states and can be decoded in parallel unless the library was compiled with NONTHREADSAFE_PSEUDOSTACK defined.

typedef struct OpusDecoder OpusDecoder

Opus decoder state. This contains the complete state of an Opus decoder. It is position independent and can be freely copied.

See also

opus_decoder_create,opus_decoder_init

typedef struct OpusDRED OpusDRED

Opus DRED state. This contains the complete state of an Opus DRED packet. It is position independent and can be freely copied.

See also

opus_dred_create,opus_dred_init

typedef struct OpusDREDDecoder OpusDREDDecoder

Opus DRED decoder. This contains the complete state of an Opus DRED decoder. It is position independent and can be freely copied.

See also

opus_dred_decoder_create,opus_dred_decoder_init

Decode an Opus packet.

Parameters

st OpusDecoder*: Decoder state
data char*: Input payload. Use a NULL pointer to indicate packet loss
len opus_int32: Number of bytes in payload*
pcm opus_int16*: Output signal (interleaved if 2 channels). length is frame_size*channels*sizeof(opus_int16)
frame_size Number of samples per channel of available space in pcm. If this is less than the maximum packet duration (120ms; 5760 for 48kHz), this function will not be capable of decoding some packets. In the case of PLC (data==NULL) or FEC (decode_fec=1), then frame_size needs to be exactly the duration of audio that is missing, otherwise the decoder will not be in the optimal state to decode the next incoming packet. For the PLC and FEC cases, frame_size must be a multiple of 2.5 ms.
decode_fec int: Flag (0 or 1) to request that any in-band forward error correction data be decoded. If no such data is available, the frame is decoded as if it were lost.

Returns

Number of decoded samples or Error codes

Decode an Opus packet with floating point output.

Parameters

st OpusDecoder*: Decoder state
data char*: Input payload. Use a NULL pointer to indicate packet loss
len opus_int32: Number of bytes in payload
pcm float*: Output signal (interleaved if 2 channels). length is frame_size*channels*sizeof(float)
frame_size Number of samples per channel of available space in pcm. If this is less than the maximum packet duration (120ms; 5760 for 48kHz), this function will not be capable of decoding some packets. In the case of PLC (data==NULL) or FEC (decode_fec=1), then frame_size needs to be exactly the duration of audio that is missing, otherwise the decoder will not be in the optimal state to decode the next incoming packet. For the PLC and FEC cases, frame_size must be a multiple of 2.5 ms.
decode_fec int: Flag (0 or 1) to request that any in-band forward error correction data be decoded. If no such data is available the frame is decoded as if it were lost.

Returns

Number of decoded samples or Error codes

OpusDecoder * opus_decoder_create (opus_int32 Fs, int channels, int * error)

Allocates and initializes a decoder state.

Parameters

Fs opus_int32: Sample rate to decode at (Hz). This must be one of 8000, 12000, 16000, 24000, or 48000.
channels int: Number of channels (1 or 2) to decode
error int*: OPUS_OK Success or Error codes

Internally Opus stores data at 48000 Hz, so that should be the default value for Fs. However, the decoder can efficiently decode to buffers at 8, 12, 16, and 24 kHz so if for some reason the caller cannot use data at the full sample rate, or knows the compressed data doesn't use the full frequency range, it can request decoding at a reduced rate. Likewise, the decoder is capable of filling in either mono or interleaved stereo pcm buffers, at the caller's request.

Perform a CTL function on an Opus decoder. Generally the request and subsequent arguments are generated by a convenience macro.

Parameters

st OpusDecoder*: Decoder state.
request This and all remaining parameters should be replaced by one of the convenience macros in Generic CTLs or Decoder related CTLs.

See also

Generic CTLs

Decoder related CTLs

Frees an OpusDecoder allocated by opus_decoder_create().

Parameters

st OpusDecoder*: State to be freed.

Decode audio from an Opus DRED packet with floating point output.

Parameters

st OpusDecoder*: Decoder state
dred OpusDRED*: DRED state
dred_offset opus_int32: position of the redundancy to decode (in samples before the beginning of the real audio data in the packet).
pcm opus_int16*: Output signal (interleaved if 2 channels). length is frame_size*channels*sizeof(opus_int16)
frame_size Number of samples per channel to decode in pcm. frame_size must be a multiple of 2.5 ms.

Returns

Number of decoded samples or Error codes

Decode audio from an Opus DRED packet with floating point output.

Parameters

st OpusDecoder*: Decoder state
dred OpusDRED*: DRED state
dred_offset opus_int32: position of the redundancy to decode (in samples before the beginning of the real audio data in the packet).
pcm float*: Output signal (interleaved if 2 channels). length is frame_size*channels*sizeof(float)
frame_size Number of samples per channel to decode in pcm. frame_size must be a multiple of 2.5 ms.

Returns

Number of decoded samples or Error codes

Gets the number of samples of an Opus packet.

Parameters

dec OpusDecoder*: Decoder state
packet char*: Opus packet
len opus_int32: Length of packet

Returns

Number of samples

Return values

OPUS_BAD_ARG Insufficient data was passed to the function
OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type

Gets the size of an OpusDecoder structure.

Parameters

channels int: Number of channels. This must be 1 or 2.

Returns

The size in bytes.

Initializes a previously allocated decoder state. The state must be at least the size returned by opus_decoder_get_size(). This is intended for applications which use their own allocator instead of malloc.

See also

opus_decoder_create,opus_decoder_get_size To reset a previously initialized state, use the OPUS_RESET_STATE CTL.

Parameters

st OpusDecoder*: Decoder state.
Fs opus_int32: Sampling rate to decode to (Hz). This must be one of 8000, 12000, 16000, 24000, or 48000.
channels int: Number of channels (1 or 2) to decode

Return values

OPUS_OK Success or Error codes

OpusDRED * opus_dred_alloc (int * error)

Allocates and initializes a DRED state.

Parameters

error int*: OPUS_OK Success or Error codes

OpusDREDDecoder * opus_dred_decoder_create (int * error)

Allocates and initializes an OpusDREDDecoder state.

Parameters

error int*: OPUS_OK Success or Error codes

Perform a CTL function on an Opus DRED decoder. Generally the request and subsequent arguments are generated by a convenience macro.

Parameters

dred_dec OpusDREDDecoder*: DRED Decoder state.
request This and all remaining parameters should be replaced by one of the convenience macros in Generic CTLs or Decoder related CTLs.

See also

Generic CTLs

Decoder related CTLs

Frees an OpusDREDDecoder allocated by opus_dred_decoder_create().

Parameters

dec OpusDREDDecoder*: State to be freed.

Gets the size of an OpusDREDDecoder structure.

Returns

The size in bytes.

Initializes an OpusDREDDecoder state.

Parameters

dec OpusDREDDecoder*: State to be initialized.

Frees an OpusDRED allocated by opus_dred_create().

Parameters

dec OpusDRED*: State to be freed.

Gets the size of an OpusDRED structure.

Returns

The size in bytes.

Decode an Opus DRED packet.

Parameters

dred_dec OpusDRED*: DRED Decoder state
dred OpusDRED*: DRED state
data char*: Input payload
len opus_int32: Number of bytes in payload
max_dred_samples opus_int32: Maximum number of DRED samples that may be needed (if available in the packet).
sampling_rate opus_int32: Sampling rate used for max_dred_samples argument. Needs not match the actual sampling rate of the decoder.
dred_end opus_int32*: Number of non-encoded (silence) samples between the DRED timestamp and the last DRED sample.
defer_processing int: Flag (0 or 1). If set to one, the CPU-intensive part of the DRED decoding is deferred until opus_dred_process() is called.

Returns

Offset (positive) of the first decoded DRED samples, zero if no DRED is present, or Error codes

Finish decoding an Opus DRED packet. The function only needs to be called if opus_dred_parse() was called with defer_processing=1. The source and destination will often be the same DRED state.

Parameters

dred_dec OpusDRED*: DRED Decoder state
src OpusDRED*: Source DRED state to start the processing from.
dst OpusDRED*: Destination DRED state to store the updated state after processing.

Returns

Error codes

Gets the bandwidth of an Opus packet.

Parameters

data char*: Opus packet

Return values

OPUS_BANDWIDTH_NARROWBAND Narrowband (4kHz bandpass)
OPUS_BANDWIDTH_MEDIUMBAND Mediumband (6kHz bandpass)
OPUS_BANDWIDTH_WIDEBAND Wideband (8kHz bandpass)
OPUS_BANDWIDTH_SUPERWIDEBAND Superwideband (12kHz bandpass)
OPUS_BANDWIDTH_FULLBAND Fullband (20kHz bandpass)
OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type

Gets the number of channels from an Opus packet.

Parameters

data char*: Opus packet

Returns

Number of channels

Return values

OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type

Gets the number of frames in an Opus packet.

Parameters

packet char*: Opus packet
len opus_int32: Length of packet

Returns

Number of frames

Return values

OPUS_BAD_ARG Insufficient data was passed to the function
OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type

Gets the number of samples of an Opus packet.

Parameters

packet char*: Opus packet
len opus_int32: Length of packet
Fs opus_int32: Sampling rate in Hz. This must be a multiple of 400, or inaccurate results will be returned.

Returns

Number of samples

Return values

OPUS_BAD_ARG Insufficient data was passed to the function
OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type

Gets the number of samples per frame from an Opus packet.

Parameters

data char*: Opus packet. This must contain at least one byte of data.
Fs opus_int32: Sampling rate in Hz. This must be a multiple of 400, or inaccurate results will be returned.

Returns

Number of samples per frame.

Checks whether an Opus packet has LBRR.

Parameters

packet char*: Opus packet
len opus_int32: Length of packet

Returns

1 is LBRR is present, 0 otherwise

Return values

OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type

Parse an opus packet into one or more frames. Opus_decode will perform this operation internally so most applications do not need to use this function. This function does not copy the frames, the returned pointers are pointers into the input packet.

Parameters

data char*: Opus packet to be parsed
len opus_int32: size of data
out_toc char*: TOC pointer
frames char*[48] encapsulated frames
size opus_int16[48] sizes of the encapsulated frames
payload_offset int*: returns the position of the payload within the packet (in bytes)

Returns

number of frames

Applies soft-clipping to bring a float signal within the [-1,1] range. If the signal is already in that range, nothing is done. If there are values outside of [-1,1], then the signal is clipped as smoothly as possible to both fit in the range and avoid creating excessive distortion in the process.

Parameters

pcm float*: Input PCM and modified PCM
frame_size int Number of samples per channel to process
channels int: Number of channels
softclip_mem float*: State memory for the soft clipping process (one float per channel, initialized to zero)

Generated automatically by Doxygen for Opus from the source code.

Wed Jul 3 2024 11:41:33 Version 1.5.2