@chapter Syntax
@c man begin SYNTAX
This section documents the syntax and formats employed by the FFmpeg
libraries and tools.
@anchor{quoting_and_escaping}
@section Quoting and escaping
FFmpeg adopts the following quoting and escaping mechanism, unless
explicitly specified. The following rules are applied:
@itemize
@item
@code{'} and @code{\} 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.
@item
A special character is escaped by prefixing it with a '\'.
@item
All characters enclosed between '' are included literally in the
parsed string. The quote character @code{'} itself cannot be quoted,
so you may need to close the quote and escape it.
@item
Leading and trailing whitespaces, unless escaped or quoted, are
removed from the parsed string.
@end itemize
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 @code{av_get_token} defined in
@file{libavutil/avstring.h} can be used to parse a token quoted or
escaped according to the rules defined above.
The tool @file{tools/ffescape} in the FFmpeg source tree can be used
to automatically quote or escape a string in a script.
@subsection Examples
@itemize
@item
Escape the string @code{Crime d'Amour} containing the @code{'} special
character:
@example
Crime d\'Amour
@end example
@item
The string above contains a quote, so the @code{'} needs to be escaped
when quoting it:
@example
'Crime d'\''Amour'
@end example
@item
Include leading or trailing whitespaces using quoting:
@example
' this string starts and ends with whitespaces '
@end example
@item
Escaping and quoting can be mixed together:
@example
' The string '\'string\'' is a string '
@end example
@item
To include a literal @code{\} you can use either escaping or quoting:
@example
'c:\foo' can be written as c:\\foo
@end example
@end itemize
@anchor{date syntax}
@section Date
The accepted syntax is:
@example
[(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...]]])|(HHMMSS[.m...]]]))[Z]
now
@end example
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.
@anchor{time duration syntax}
@section Time duration
The accepted syntax is:
@example
[-][HH:]MM:SS[.m...]
[-]S+[.m...]
@end example
@var{HH} expresses the number of hours, @var{MM} the number a of minutes
and @var{SS} the number of seconds.
@anchor{video size syntax}
@section Video size
Specify the size of the sourced video, it may be a string of the form
@var{width}x@var{height}, or the name of a size abbreviation.
The following abbreviations are recognized:
@table @samp
@item ntsc
720x480
@item pal
720x576
@item qntsc
352x240
@item qpal
352x288
@item sntsc
640x480
@item spal
768x576
@item film
352x240
@item ntsc-film
352x240
@item sqcif
128x96
@item qcif
176x144
@item cif
352x288
@item 4cif
704x576
@item 16cif
1408x1152
@item qqvga
160x120
@item qvga
320x240
@item vga
640x480
@item svga
800x600
@item xga
1024x768
@item uxga
1600x1200
@item qxga
2048x1536
@item sxga
1280x1024
@item qsxga
2560x2048
@item hsxga
5120x4096
@item wvga
852x480
@item wxga
1366x768
@item wsxga
1600x1024
@item wuxga
1920x1200
@item woxga
2560x1600
@item wqsxga
3200x2048
@item wquxga
3840x2400
@item whsxga
6400x4096
@item whuxga
7680x4800
@item cga
320x200
@item ega
640x350
@item hd480
852x480
@item hd720
1280x720
@item hd1080
1920x1080
@item 2k
2048x1080
@item 2kflat
1998x1080
@item 2kscope
2048x858
@item 4k
4096x2160
@item 4kflat
3996x2160
@item 4kscope
4096x1716
@end table
@anchor{video rate syntax}
@section Video rate
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
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation.
The following abbreviations are recognized:
@table @samp
@item ntsc
30000/1001
@item pal
25/1
@item qntsc
30000/1001
@item qpal
25/1
@item sntsc
30000/1001
@item spal
25/1
@item film
24/1
@item ntsc-film
24000/1001
@end table
@anchor{ratio syntax}
@section Ratio
A ratio can be expressed as an expression, or in the form
@var{numerator}:@var{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.
@anchor{color syntax}
@section Color
It can be the name of a color (case insensitive match) or a
[0x|#]RRGGBB[AA] sequence, possibly followed by "@@" and a string
representing the alpha component.
The alpha component may be a string composed by "0x" followed by an
hexadecimal number or a decimal number between 0.0 and 1.0, which
represents the opacity value (0x00/0.0 means completely transparent,
0xff/1.0 completely opaque).
If the alpha component is not specified then 0xff is assumed.
The string "random" will result in a random color.
@c man end SYNTAX
@chapter Expression Evaluation
@c man begin EXPRESSION EVALUATION
When evaluating an arithmetic expression, FFmpeg uses an internal
formula evaluator, implemented through the @file{libavutil/eval.h}
interface.
An expression may contain unary, binary operators, constants, and
functions.
Two expressions @var{expr1} and @var{expr2} can be combined to form
another expression "@var{expr1};@var{expr2}".
@var{expr1} and @var{expr2} are evaluated in turn, and the new
expression evaluates to the value of @var{expr2}.
The following binary operators are available: @code{+}, @code{-},
@code{*}, @code{/}, @code{^}.
The following unary operators are available: @code{+}, @code{-}.
The following functions are available:
@table @option
@item abs(x)
Compute absolute value of @var{x}.
@item acos(x)
Compute arccosine of @var{x}.
@item asin(x)
Compute arcsine of @var{x}.
@item atan(x)
Compute arctangent of @var{x}.
@item between(x, min, max)
Return 1 if @var{x} is greater than or equal to @var{min} and lesser than or
equal to @var{max}, 0 otherwise.
@item bitand(x, y)
@item bitor(x, y)
Compute bitwise and/or operation on @var{x} and @var{y}.
The results of the evaluation of @var{x} and @var{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).
@item ceil(expr)
Round the value of expression @var{expr} upwards to the nearest
integer. For example, "ceil(1.5)" is "2.0".
@item cos(x)
Compute cosine of @var{x}.
@item cosh(x)
Compute hyperbolic cosine of @var{x}.
@item eq(x, y)
Return 1 if @var{x} and @var{y} are equivalent, 0 otherwise.
@item exp(x)
Compute exponential of @var{x} (with base @code{e}, the Euler's number).
@item floor(expr)
Round the value of expression @var{expr} downwards to the nearest
integer. For example, "floor(-1.5)" is "-2.0".
@item gauss(x)
Compute Gauss function of @var{x}, corresponding to
@code{exp(-x*x/2) / sqrt(2*PI)}.
@item gcd(x, y)
Return the greatest common divisor of @var{x} and @var{y}. If both @var{x} and
@var{y} are 0 or either or both are less than zero then behavior is undefined.
@item gt(x, y)
Return 1 if @var{x} is greater than @var{y}, 0 otherwise.
@item gte(x, y)
Return 1 if @var{x} is greater than or equal to @var{y}, 0 otherwise.
@item hypot(x, y)
This function is similar to the C function with the same name; it returns
"sqrt(@var{x}*@var{x} + @var{y}*@var{y})", the length of the hypotenuse of a
right triangle with sides of length @var{x} and @var{y}, or the distance of the
point (@var{x}, @var{y}) from the origin.
@item if(x, y)
Evaluate @var{x}, and if the result is non-zero return the result of
the evaluation of @var{y}, return 0 otherwise.
@item if(x, y, z)
Evaluate @var{x}, and if the result is non-zero return the evaluation
result of @var{y}, otherwise the evaluation result of @var{z}.
@item ifnot(x, y)
Evaluate @var{x}, and if the result is zero return the result of the
evaluation of @var{y}, return 0 otherwise.
@item ifnot(x, y, z)
Evaluate @var{x}, and if the result is zero return the evaluation
result of @var{y}, otherwise the evaluation result of @var{z}.
@item isinf(x)
Return 1.0 if @var{x} is +/-INFINITY, 0.0 otherwise.
@item isnan(x)
Return 1.0 if @var{x} is NAN, 0.0 otherwise.
@item ld(var)
Allow to load the value of the internal variable with number
@var{var}, which was previously stored with st(@var{var}, @var{expr}).
The function returns the loaded value.
@item log(x)
Compute natural logarithm of @var{x}.
@item lt(x, y)
Return 1 if @var{x} is lesser than @var{y}, 0 otherwise.
@item lte(x, y)
Return 1 if @var{x} is lesser than or equal to @var{y}, 0 otherwise.
@item max(x, y)
Return the maximum between @var{x} and @var{y}.
@item min(x, y)
Return the maximum between @var{x} and @var{y}.
@item mod(x, y)
Compute the remainder of division of @var{x} by @var{y}.
@item not(expr)
Return 1.0 if @var{expr} is zero, 0.0 otherwise.
@item pow(x, y)
Compute the power of @var{x} elevated @var{y}, it is equivalent to
"(@var{x})^(@var{y})".
@item print(t)
@item print(t, l)
Print the value of expression @var{t} with loglevel @var{l}. If
@var{l} is not specified then a default log level is used.
Returns the value of the expression printed.
Prints t with loglevel l
@item random(x)
Return a pseudo random value between 0.0 and 1.0. @var{x} is the index of the
internal variable which will be used to save the seed/state.
@item root(expr, max)
Find an input value for which the function represented by @var{expr}
with argument @var{ld(0)} is 0 in the interval 0..@var{max}.
The expression in @var{expr} must denote a continuous function or the
result is undefined.
@var{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
@code{ld(0)}. When the expression evaluates to 0 then the
corresponding input value will be returned.
@item sin(x)
Compute sine of @var{x}.
@item sinh(x)
Compute hyperbolic sine of @var{x}.
@item sqrt(expr)
Compute the square root of @var{expr}. This is equivalent to
"(@var{expr})^.5".
@item squish(x)
Compute expression @code{1/(1 + exp(4*x))}.
@item st(var, expr)
Allow to store the value of the expression @var{expr} in an internal
variable. @var{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.
@item tan(x)
Compute tangent of @var{x}.
@item tanh(x)
Compute hyperbolic tangent of @var{x}.
@item taylor(expr, x)
@item taylor(expr, x, id)
Evaluate a Taylor series at @var{x}, given an expression representing
the @code{ld(id)}-th derivative of a function at 0.
When the series does not converge the result is undefined.
@var{ld(id)} is used to represent the derivative order in @var{expr},
which means that the given expression will be evaluated multiple times
with various input values that the expression can access through
@code{ld(id)}. If @var{id} is not specified then 0 is assumed.
Note, when you have the derivatives at y instead of 0,
@code{taylor(expr, x-y)} can be used.
@item time(0)
Return the current (wallclock) time in seconds.
@item trunc(expr)
Round the value of expression @var{expr} towards zero to the nearest
integer. For example, "trunc(-1.5)" is "-1.0".
@item while(cond, expr)
Evaluate expression @var{expr} while the expression @var{cond} is
non-zero, and returns the value of the last @var{expr} evaluation, or
NAN if @var{cond} was always false.
@end table
The following constants are available:
@table @option
@item PI
area of the unit disc, approximately 3.14
@item E
exp(1) (Euler's number), approximately 2.718
@item PHI
golden ratio (1+sqrt(5))/2, approximately 1.618
@end table
Assuming that an expression is considered "true" if it has a non-zero
value, note that:
@code{*} works like AND
@code{+} works like OR
For example the construct:
@example
if (A AND B) then C
@end example
is equivalent to:
@example
if(A*B, C)
@end example
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.
@table @option
@item y
10^-24 / 2^-80
@item z
10^-21 / 2^-70
@item a
10^-18 / 2^-60
@item f
10^-15 / 2^-50
@item p
10^-12 / 2^-40
@item n
10^-9 / 2^-30
@item u
10^-6 / 2^-20
@item m
10^-3 / 2^-10
@item c
10^-2
@item d
10^-1
@item h
10^2
@item k
10^3 / 2^10
@item K
10^3 / 2^10
@item M
10^6 / 2^20
@item G
10^9 / 2^30
@item T
10^12 / 2^40
@item P
10^15 / 2^40
@item E
10^18 / 2^50
@item Z
10^21 / 2^60
@item Y
10^24 / 2^70
@end table
@c man end
@chapter OpenCL Options
@c man begin OPENCL OPTIONS
When FFmpeg is configured with @code{--enable-opencl}, it is possible
to set the options for the global OpenCL context.
The list of supported options follows:
@table @option
@item build_options
Set build options used to compile the registered kernels.
See reference "OpenCL Specification Version: 1.2 chapter 5.6.4".
@item platform_idx
Select the index of the platform to run OpenCL code.
The specified index must be one of the indexes in the device list
which can be obtained with @code{av_opencl_get_device_list()}.
@item device_idx
Select the index of the device used to run OpenCL code.
The specifed index must be one of the indexes in the device list which
can be obtained with @code{av_opencl_get_device_list()}.
@end table
@c man end OPENCL OPTIONS