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@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

There are two accepted syntaxes for expressing time duration.

@example

[-][@var{HH}:]@var{MM}:@var{SS}[.@var{m}...]

@end example

@var{HH} expresses the number of hours, @var{MM} the number of minutes

for a maximum of 2 digits, and @var{SS} the number of seconds for a

maximum of 2 digits. The @var{m} at the end expresses decimal value for

@var{SS}.

@emph{or}

@example

[-]@var{S}+[.@var{m}...]

@end example

@var{S} expresses the number of seconds, with the optional decimal part

@var{m}.

In both expressions, the optional @samp{-} indicates negative duration.

@subsection Examples

The following examples are all valid time duration:

@table @samp

@item 55

55 seconds

@item 12:03:45

12 hours, 03 minutes and 45 seconds

@item 23.189

23.189 seconds

@end table

@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

@item nhd

640x360

@item hqvga

240x160

@item wqvga

400x240

@item fwqvga

432x240

@item hvga

480x320

@item qhd

960x540

@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 as defined below (case insensitive match) or a

@code{[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 (@samp{0x00} or @samp{0.0} means completely

transparent, @samp{0xff} or @samp{1.0} completely opaque). If the alpha

component is not specified then @samp{0xff} is assumed.

The string @samp{random} will result in a random color.

The following names of colors are recognized:

@table @samp

@item AliceBlue

0xF0F8FF

@item AntiqueWhite

0xFAEBD7

@item Aqua

0x00FFFF

@item Aquamarine

0x7FFFD4

@item Azure

0xF0FFFF

@item Beige

0xF5F5DC

@item Bisque

0xFFE4C4

@item Black

0x000000

@item BlanchedAlmond

0xFFEBCD

@item Blue

0x0000FF

@item BlueViolet

0x8A2BE2

@item Brown

0xA52A2A

@item BurlyWood

0xDEB887

@item CadetBlue

0x5F9EA0

@item Chartreuse

0x7FFF00

@item Chocolate

0xD2691E

@item Coral

0xFF7F50

@item CornflowerBlue

0x6495ED

@item Cornsilk

0xFFF8DC

@item Crimson

0xDC143C

@item Cyan

0x00FFFF

@item DarkBlue

0x00008B

@item DarkCyan

0x008B8B

@item DarkGoldenRod

0xB8860B

@item DarkGray

0xA9A9A9

@item DarkGreen

0x006400

@item DarkKhaki

0xBDB76B

@item DarkMagenta

0x8B008B

@item DarkOliveGreen

0x556B2F

@item Darkorange

0xFF8C00

@item DarkOrchid

0x9932CC

@item DarkRed

0x8B0000

@item DarkSalmon

0xE9967A

@item DarkSeaGreen

0x8FBC8F

@item DarkSlateBlue

0x483D8B

@item DarkSlateGray

0x2F4F4F

@item DarkTurquoise

0x00CED1

@item DarkViolet

0x9400D3

@item DeepPink

0xFF1493

@item DeepSkyBlue

0x00BFFF

@item DimGray

0x696969

@item DodgerBlue

0x1E90FF

@item FireBrick

0xB22222

@item FloralWhite

0xFFFAF0

@item ForestGreen

0x228B22

@item Fuchsia

0xFF00FF

@item Gainsboro

0xDCDCDC

@item GhostWhite

0xF8F8FF

@item Gold

0xFFD700

@item GoldenRod

0xDAA520

@item Gray

0x808080

@item Green

0x008000

@item GreenYellow

0xADFF2F

@item HoneyDew

0xF0FFF0

@item HotPink

0xFF69B4

@item IndianRed

0xCD5C5C

@item Indigo

0x4B0082

@item Ivory

0xFFFFF0

@item Khaki

0xF0E68C

@item Lavender

0xE6E6FA

@item LavenderBlush

0xFFF0F5

@item LawnGreen

0x7CFC00

@item LemonChiffon

0xFFFACD

@item LightBlue

0xADD8E6

@item LightCoral

0xF08080

@item LightCyan

0xE0FFFF

@item LightGoldenRodYellow

0xFAFAD2

@item LightGreen

0x90EE90

@item LightGrey

0xD3D3D3

@item LightPink

0xFFB6C1

@item LightSalmon

0xFFA07A

@item LightSeaGreen

0x20B2AA

@item LightSkyBlue

0x87CEFA

@item LightSlateGray

0x778899

@item LightSteelBlue

0xB0C4DE

@item LightYellow

0xFFFFE0

@item Lime

0x00FF00

@item LimeGreen

0x32CD32

@item Linen

0xFAF0E6

@item Magenta

0xFF00FF

@item Maroon

0x800000

@item MediumAquaMarine

0x66CDAA

@item MediumBlue

0x0000CD

@item MediumOrchid

0xBA55D3

@item MediumPurple

0x9370D8

@item MediumSeaGreen

0x3CB371

@item MediumSlateBlue

0x7B68EE

@item MediumSpringGreen

0x00FA9A

@item MediumTurquoise

0x48D1CC

@item MediumVioletRed

0xC71585

@item MidnightBlue

0x191970

@item MintCream

0xF5FFFA

@item MistyRose

0xFFE4E1

@item Moccasin

0xFFE4B5

@item NavajoWhite

0xFFDEAD

@item Navy

0x000080

@item OldLace

0xFDF5E6

@item Olive

0x808000

@item OliveDrab

0x6B8E23

@item Orange

0xFFA500

@item OrangeRed

0xFF4500

@item Orchid

0xDA70D6

@item PaleGoldenRod

0xEEE8AA

@item PaleGreen

0x98FB98

@item PaleTurquoise

0xAFEEEE

@item PaleVioletRed

0xD87093

@item PapayaWhip

0xFFEFD5

@item PeachPuff

0xFFDAB9

@item Peru

0xCD853F

@item Pink

0xFFC0CB

@item Plum

0xDDA0DD

@item PowderBlue

0xB0E0E6

@item Purple

0x800080

@item Red

0xFF0000

@item RosyBrown

0xBC8F8F

@item RoyalBlue

0x4169E1

@item SaddleBrown

0x8B4513

@item Salmon

0xFA8072

@item SandyBrown

0xF4A460

@item SeaGreen

0x2E8B57

@item SeaShell

0xFFF5EE

@item Sienna

0xA0522D

@item Silver

0xC0C0C0

@item SkyBlue

0x87CEEB

@item SlateBlue

0x6A5ACD

@item SlateGray

0x708090

@item Snow

0xFFFAFA

@item SpringGreen

0x00FF7F

@item SteelBlue

0x4682B4

@item Tan

0xD2B48C

@item Teal

0x008080

@item Thistle

0xD8BFD8

@item Tomato

0xFF6347

@item Turquoise

0x40E0D0

@item Violet

0xEE82EE

@item Wheat

0xF5DEB3

@item White

0xFFFFFF

@item WhiteSmoke

0xF5F5F5

@item Yellow

0xFFFF00

@item YellowGreen

0x9ACD32

@end table

@anchor{channel layout syntax}

@section Channel Layout

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:

@table @samp

@item FL

front left

@item FR

front right

@item FC

front center

@item LFE

low frequency

@item BL

back left

@item BR

back right

@item FLC

front left-of-center

@item FRC

front right-of-center

@item BC

back center

@item SL

side left

@item SR

side right

@item TC

top center

@item TFL

top front left

@item TFC

top front center

@item TFR

top front right

@item TBL

top back left

@item TBC

top back center

@item TBR

top back right

@item DL

downmix left

@item DR

downmix right

@item WL

wide left

@item WR

wide right

@item SDL

surround direct left

@item SDR

surround direct right

@item LFE2

low frequency 2

@end table

Standard channel layout compositions can be specified by using the

following identifiers:

@table @samp

@item mono

FC

@item stereo

FL+FR

@item 2.1

FL+FR+LFE

@item 3.0

FL+FR+FC

@item 3.0(back)

FL+FR+BC

@item 4.0

FL+FR+FC+BC

@item quad

FL+FR+BL+BR

@item quad(side)

FL+FR+SL+SR

@item 3.1

FL+FR+FC+LFE

@item 5.0

FL+FR+FC+BL+BR

@item 5.0(side)

FL+FR+FC+SL+SR

@item 4.1

FL+FR+FC+LFE+BC

@item 5.1

FL+FR+FC+LFE+BL+BR

@item 5.1(side)

FL+FR+FC+LFE+SL+SR

@item 6.0

FL+FR+FC+BC+SL+SR

@item 6.0(front)

FL+FR+FLC+FRC+SL+SR

@item hexagonal

FL+FR+FC+BL+BR+BC

@item 6.1

FL+FR+FC+LFE+BC+SL+SR

@item 6.1

FL+FR+FC+LFE+BL+BR+BC

@item 6.1(front)

FL+FR+LFE+FLC+FRC+SL+SR

@item 7.0

FL+FR+FC+BL+BR+SL+SR

@item 7.0(front)

FL+FR+FC+FLC+FRC+SL+SR

@item 7.1

FL+FR+FC+LFE+BL+BR+SL+SR

@item 7.1(wide)

FL+FR+FC+LFE+BL+BR+FLC+FRC

@item 7.1(wide-side)

FL+FR+FC+LFE+FLC+FRC+SL+SR

@item octagonal

FL+FR+FC+BL+BR+BC+SL+SR

@item downmix

DL+DR

@end table

A custom channel layout can be specified as a sequence of terms, separated by

'+' or '|'. Each term can be:

@itemize

@item

the name of a standard channel layout (e.g. @samp{mono},

@samp{stereo}, @samp{4.0}, @samp{quad}, @samp{5.0}, etc.)

@item

the name of a single channel (e.g. @samp{FL}, @samp{FR}, @samp{FC}, @samp{LFE}, etc.)

@item

a number of channels, in decimal, optionally followed by 'c', yielding

the default channel layout for that number of channels (see the

function @code{av_get_default_channel_layout})

@item

a channel layout mask, in hexadecimal starting with "0x" (see the

@code{AV_CH_*} macros in @file{libavutil/channel_layout.h}.

@end itemize

Starting from libavutil version 53 the trailing character "c" to

specify a number of channels will be required, while a channel layout

mask could also be specified as a decimal number (if and only if not

followed by "c").

See also the function @code{av_get_channel_layout} defined in

@file{libavutil/channel_layout.h}.

@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