ffmpeg-utils - FFmpeg utilities
This document describes some generic features and utilities
provided by the libavutil library.
This section documents the syntax and formats employed by the
FFmpeg libraries and tools.
FFmpeg adopts the following quoting and escaping mechanism, unless
explicitly specified. The following rules are applied:
- ' and \ are special characters (respectively used for
quoting and escaping). In addition to them, there might be other special
characters depending on the specific syntax where the escaping and quoting
are employed.
- A special character is escaped by prefixing it with a \.
- All characters enclosed between '' are included literally in the
parsed string. The quote character ' itself cannot be quoted, so
you may need to close the quote and escape it.
- Leading and trailing whitespaces, unless escaped or quoted, are removed
from the parsed string.
Note that you may need to add a second level of escaping when
using the command line or a script, which depends on the syntax of the
adopted shell language.
The function "av_get_token"
defined in libavutil/avstring.h can be used to parse a token quoted
or escaped according to the rules defined above.
The tool tools/ffescape in the FFmpeg source tree can be
used to automatically quote or escape a string in a script.
Examples
- Escape the string "Crime d'Amour"
containing the "'" special character:
Crime d\'Amour
- The string above contains a quote, so the
"'" needs to be escaped when quoting it:
'Crime d'\''Amour'
- Include leading or trailing whitespaces using quoting:
' this string starts and ends with whitespaces '
- Escaping and quoting can be mixed together:
' The string '\'string\'' is a string '
- To include a literal \ you can use either escaping or quoting:
'c:\foo' can be written as c:\\foo
The accepted syntax is:
[(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...]]])|(HHMMSS[.m...]]]))[Z]
now
If the value is "now" it takes the current time.
Time is local time unless Z is appended, in which case it is
interpreted as UTC. If the year-month-day part is not specified it takes the
current year-month-day.
There are two accepted syntaxes for expressing time duration.
[-][<HH>:]<MM>:<SS>[.<m>...]
HH expresses the number of hours, MM the number of
minutes for a maximum of 2 digits, and SS the number of seconds for a
maximum of 2 digits. The m at the end expresses decimal value for
SS.
or
[-]<S>+[.<m>...][s|ms|us]
S expresses the number of seconds, with the optional
decimal part m. The optional literal suffixes s, ms or
us indicate to interpret the value as seconds, milliseconds or
microseconds, respectively.
In both expressions, the optional - indicates negative
duration.
Examples
The following examples are all valid time duration:
- 55
- 55 seconds
- 0.2
- 0.2 seconds
- 200ms
- 200 milliseconds, that's 0.2s
- 200000us
- 200000 microseconds, that's 0.2s
- 12:03:45
- 12 hours, 03 minutes and 45 seconds
- 23.189
- 23.189 seconds
Specify the frame rate of a video, expressed as the number of
frames generated per second. It has to be a string in the format
frame_rate_num/frame_rate_den, an integer number, a float
number or a valid video frame rate abbreviation.
The following abbreviations are recognized:
- ntsc
- 30000/1001
- pal
- 25/1
- qntsc
- 30000/1001
- qpal
- 25/1
- sntsc
- 30000/1001
- spal
- 25/1
- film
- 24/1
- ntsc-film
- 24000/1001
A ratio can be expressed as an expression, or in the form
numerator:denominator.
Note that a ratio with infinite (1/0) or negative value is
considered valid, so you should check on the returned value if you want to
exclude those values.
The undefined value can be expressed using the "0:0"
string.
A channel layout specifies the spatial disposition of the channels
in a multi-channel audio stream. To specify a channel layout, FFmpeg makes
use of a special syntax.
Individual channels are identified by an id, as given by the table
below:
- FL
- front left
- FR
- front right
- FC
- front center
- LFE
- low frequency
- BL
- back left
- BR
- back right
- FLC
- front left-of-center
- FRC
- front right-of-center
- BC
- back center
- SL
- side left
- SR
- side right
- TC
- top center
- TFL
- top front left
- TFC
- top front center
- TFR
- top front right
- TBL
- top back left
- TBC
- top back center
- TBR
- top back right
- DL
- downmix left
- DR
- downmix right
- WL
- wide left
- WR
- wide right
- SDL
- surround direct left
- SDR
- surround direct right
- LFE2
- low frequency 2
Standard channel layout compositions can be specified by using the
following identifiers:
- mono
- FC
- stereo
- FL+FR
- 2.1
- FL+FR+LFE
- 3.0
- FL+FR+FC
- 3.0(back)
- FL+FR+BC
- 4.0
- FL+FR+FC+BC
- quad
- FL+FR+BL+BR
- quad(side)
- FL+FR+SL+SR
- 3.1
- FL+FR+FC+LFE
- 5.0
- FL+FR+FC+BL+BR
- 5.0(side)
- FL+FR+FC+SL+SR
- 4.1
- FL+FR+FC+LFE+BC
- 5.1
- FL+FR+FC+LFE+BL+BR
- 5.1(side)
- FL+FR+FC+LFE+SL+SR
- 6.0
- FL+FR+FC+BC+SL+SR
- 6.0(front)
- FL+FR+FLC+FRC+SL+SR
- hexagonal
- FL+FR+FC+BL+BR+BC
- 6.1
- FL+FR+FC+LFE+BC+SL+SR
- 6.1
- FL+FR+FC+LFE+BL+BR+BC
- 6.1(front)
- FL+FR+LFE+FLC+FRC+SL+SR
- 7.0
- FL+FR+FC+BL+BR+SL+SR
- 7.0(front)
- FL+FR+FC+FLC+FRC+SL+SR
- 7.1
- FL+FR+FC+LFE+BL+BR+SL+SR
- 7.1(wide)
- FL+FR+FC+LFE+BL+BR+FLC+FRC
- 7.1(wide-side)
- FL+FR+FC+LFE+FLC+FRC+SL+SR
- octagonal
- FL+FR+FC+BL+BR+BC+SL+SR
- hexadecagonal
- FL+FR+FC+BL+BR+BC+SL+SR+WL+WR+TBL+TBR+TBC+TFC+TFL+TFR
- downmix
- DL+DR
- 22.2
- FL+FR+FC+LFE+BL+BR+FLC+FRC+BC+SL+SR+TC+TFL+TFC+TFR+TBL+TBC+TBR+LFE2+TSL+TSR+BFC+BFL+BFR
A custom channel layout can be specified as a sequence of terms,
separated by '+'. Each term can be:
- •
- the name of a single channel (e.g. FL, FR, FC,
LFE, etc.), each optionally containing a custom name after a '@',
(e.g. FL@Left, FR@Right, FC@Center,
LFE@Low_Frequency, etc.)
A standard channel layout can be specified by the following:
- the name of a single channel (e.g. FL, FR, FC,
LFE, etc.)
- the name of a standard channel layout (e.g. mono, stereo,
4.0, quad, 5.0, etc.)
- a number of channels, in decimal, followed by 'c', yielding the default
channel layout for that number of channels (see the function
"av_channel_layout_default"). Note that
not all channel counts have a default layout.
- a number of channels, in decimal, followed by 'C', yielding an unknown
channel layout with the specified number of channels. Note that not all
channel layout specification strings support unknown channel layouts.
- a channel layout mask, in hexadecimal starting with "0x" (see
the "AV_CH_*" macros in
libavutil/channel_layout.h.
Before libavutil version 53 the trailing character "c"
to specify a number of channels was optional, but now it is required, while
a channel layout mask can also be specified as a decimal number (if and only
if not followed by "c" or "C").
See also the function
"av_channel_layout_from_string" defined in
libavutil/channel_layout.h.
When evaluating an arithmetic expression, FFmpeg uses an internal
formula evaluator, implemented through the libavutil/eval.h
interface.
An expression may contain unary, binary operators, constants, and
functions.
Two expressions expr1 and expr2 can be combined to
form another expression "expr1;expr2". expr1
and expr2 are evaluated in turn, and the new expression evaluates to
the value of expr2.
The following binary operators are available:
"+",
"-",
"*",
"/",
"^".
The following unary operators are available:
"+",
"-".
The following functions are available:
- abs(x)
- Compute absolute value of x.
- acos(x)
- Compute arccosine of x.
- asin(x)
- Compute arcsine of x.
- atan(x)
- Compute arctangent of x.
- atan2(x,
y)
- Compute principal value of the arc tangent of y/x.
- between(x, min,
max)
- Return 1 if x is greater than or equal to min and lesser
than or equal to max, 0 otherwise.
- bitand(x,
y)
- bitor(x,
y)
- Compute bitwise and/or operation on x and y.
The results of the evaluation of x and y are
converted to integers before executing the bitwise operation.
Note that both the conversion to integer and the conversion
back to floating point can lose precision. Beware of unexpected results
for large numbers (usually 2^53 and larger).
- ceil(expr)
- Round the value of expression expr upwards to the nearest integer.
For example, "ceil(1.5)" is "2.0".
- clip(x, min,
max)
- Return the value of x clipped between min and
max.
- cos(x)
- Compute cosine of x.
- cosh(x)
- Compute hyperbolic cosine of x.
- eq(x, y)
- Return 1 if x and y are equivalent, 0 otherwise.
- exp(x)
- Compute exponential of x (with base
"e", the Euler's number).
- floor(expr)
- Round the value of expression expr downwards to the nearest
integer. For example, "floor(-1.5)" is "-2.0".
- gauss(x)
- Compute Gauss function of x, corresponding to
"exp(-x*x/2) / sqrt(2*PI)".
- gcd(x, y)
- Return the greatest common divisor of x and y. If both
x and y are 0 or either or both are less than zero then
behavior is undefined.
- gt(x, y)
- Return 1 if x is greater than y, 0 otherwise.
- gte(x, y)
- Return 1 if x is greater than or equal to y, 0
otherwise.
- hypot(x,
y)
- This function is similar to the C function with the same name; it returns
"sqrt(x*x + y*y)", the length of the
hypotenuse of a right triangle with sides of length x and y,
or the distance of the point (x, y) from the origin.
- if(x, y)
- Evaluate x, and if the result is non-zero return the result of the
evaluation of y, return 0 otherwise.
- if(x, y,
z)
- Evaluate x, and if the result is non-zero return the evaluation
result of y, otherwise the evaluation result of z.
- ifnot(x,
y)
- Evaluate x, and if the result is zero return the result of the
evaluation of y, return 0 otherwise.
- ifnot(x, y,
z)
- Evaluate x, and if the result is zero return the evaluation result
of y, otherwise the evaluation result of z.
- isinf(x)
- Return 1.0 if x is +/-INFINITY, 0.0 otherwise.
- isnan(x)
- Return 1.0 if x is NAN, 0.0 otherwise.
- ld(var)
- Load the value of the internal variable with number var, which was
previously stored with st(var, expr). The function returns
the loaded value.
- lerp(x, y,
z)
- Return linear interpolation between x and y by amount of
z.
- log(x)
- Compute natural logarithm of x.
- lt(x, y)
- Return 1 if x is lesser than y, 0 otherwise.
- lte(x, y)
- Return 1 if x is lesser than or equal to y, 0
otherwise.
- max(x, y)
- Return the maximum between x and y.
- min(x, y)
- Return the minimum between x and y.
- mod(x, y)
- Compute the remainder of division of x by y.
- not(expr)
- Return 1.0 if expr is zero, 0.0 otherwise.
- pow(x, y)
- Compute the power of x elevated y, it is equivalent to
"(x)^(y)".
- print(t)
- print(t,
l)
- Print the value of expression t with loglevel l. If l
is not specified then a default log level is used. Returns the value of
the expression printed.
Prints t with loglevel l
- random(x)
- Return a pseudo random value between 0.0 and 1.0. x is the index of
the internal variable which will be used to save the seed/state.
- root(expr,
max)
- Find an input value for which the function represented by expr with
argument ld(0) is 0 in the interval
0..max.
The expression in expr must denote a continuous
function or the result is undefined.
ld(0) is used to represent the
function input value, which means that the given expression will be
evaluated multiple times with various input values that the expression
can access through ld(0). When the expression
evaluates to 0 then the corresponding input value will be returned.
- round(expr)
- Round the value of expression expr to the nearest integer. For
example, "round(1.5)" is "2.0".
- sgn(x)
- Compute sign of x.
- sin(x)
- Compute sine of x.
- sinh(x)
- Compute hyperbolic sine of x.
- sqrt(expr)
- Compute the square root of expr. This is equivalent to
"(expr)^.5".
- squish(x)
- Compute expression "1/(1 +
exp(4*x))".
- st(var,
expr)
- Store the value of the expression expr in an internal variable.
var specifies the number of the variable where to store the value,
and it is a value ranging from 0 to 9. The function returns the value
stored in the internal variable. Note, Variables are currently not shared
between expressions.
- tan(x)
- Compute tangent of x.
- tanh(x)
- Compute hyperbolic tangent of x.
- taylor(expr,
x)
- taylor(expr,
x, id)
- Evaluate a Taylor series at x, given an expression representing the
"ld(id)"-th derivative of a function at
0.
When the series does not converge the result is undefined.
ld(id) is used to represent the derivative order in
expr, which means that the given expression will be evaluated
multiple times with various input values that the expression can access
through "ld(id)". If id is not
specified then 0 is assumed.
Note, when you have the derivatives at y instead of 0,
"taylor(expr, x-y)" can be used.
- time(0)
- Return the current (wallclock) time in seconds.
- trunc(expr)
- Round the value of expression expr towards zero to the nearest
integer. For example, "trunc(-1.5)" is "-1.0".
- while(cond,
expr)
- Evaluate expression expr while the expression cond is
non-zero, and returns the value of the last expr evaluation, or NAN
if cond was always false.
The following constants are available:
- PI
- area of the unit disc, approximately 3.14
- E
- exp(1) (Euler's number), approximately 2.718
- PHI
- golden ratio (1+sqrt(5))/2, approximately 1.618
Assuming that an expression is considered "true" if it
has a non-zero value, note that:
"*" works like AND
"+" works like OR
For example the construct:
if (A AND B) then C
is equivalent to:
if(A*B, C)
In your C code, you can extend the list of unary and binary
functions, and define recognized constants, so that they are available for
your expressions.
The evaluator also recognizes the International System unit
prefixes. If 'i' is appended after the prefix, binary prefixes are used,
which are based on powers of 1024 instead of powers of 1000. The 'B' postfix
multiplies the value by 8, and can be appended after a unit prefix or used
alone. This allows using for example 'KB', 'MiB', 'G' and 'B' as number
postfix.
The list of available International System prefixes follows, with
indication of the corresponding powers of 10 and of 2.
- y
- 10^-24 / 2^-80
- z
- 10^-21 / 2^-70
- a
- 10^-18 / 2^-60
- f
- 10^-15 / 2^-50
- p
- 10^-12 / 2^-40
- n
- 10^-9 / 2^-30
- u
- 10^-6 / 2^-20
- m
- 10^-3 / 2^-10
- c
- 10^-2
- d
- 10^-1
- h
- 10^2
- k
- 10^3 / 2^10
- K
- 10^3 / 2^10
- M
- 10^6 / 2^20
- G
- 10^9 / 2^30
- T
- 10^12 / 2^40
- P
- 10^15 / 2^40
- E
- 10^18 / 2^50
- Z
- 10^21 / 2^60
- Y
- 10^24 / 2^70
The FFmpeg developers.
For details about the authorship, see the Git history of the
project (https://git.ffmpeg.org/ffmpeg), e.g. by typing the command git
log in the FFmpeg source directory, or browsing the online repository at
<https://git.ffmpeg.org/ffmpeg>.
Maintainers for the specific components are listed in the file
MAINTAINERS in the source code tree.