Syntax
******

This section documents the syntax and formats employed by the FFmpeg libraries and tools.

Quoting and escaping
====================

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

Date
====

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.

Time duration
=============

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 expresses the number of seconds, with the optional decimal part M.

In both expressions, the optional - indicates negative duration.

Examples
--------

The following examples are all valid time duration:

55
     55 seconds

12:03:45
     12 hours, 03 minutes and 45 seconds

23.189
     23.189 seconds

Video size
==========

Specify the size of the sourced video, it may be a string of the form WIDTHxHEIGHT, or the name of a size abbreviation.

The following abbreviations are recognized:

ntsc
     720x480

pal
     720x576

qntsc
     352x240

qpal
     352x288

sntsc
     640x480

spal
     768x576

film
     352x240

ntsc-film
     352x240

sqcif
     128x96

qcif
     176x144

cif
     352x288

4cif
     704x576

16cif
     1408x1152

qqvga
     160x120

qvga
     320x240

vga
     640x480

svga
     800x600

xga
     1024x768

uxga
     1600x1200

qxga
     2048x1536

sxga
     1280x1024

qsxga
     2560x2048

hsxga
     5120x4096

wvga
     852x480

wxga
     1366x768

wsxga
     1600x1024

wuxga
     1920x1200

woxga
     2560x1600

wqsxga
     3200x2048

wquxga
     3840x2400

whsxga
     6400x4096

whuxga
     7680x4800

cga
     320x200

ega
     640x350

hd480
     852x480

hd720
     1280x720

hd1080
     1920x1080

2k
     2048x1080

2kflat
     1998x1080

2kscope
     2048x858

4k
     4096x2160

4kflat
     3996x2160

4kscope
     4096x1716

nhd
     640x360

hqvga
     240x160

wqvga
     400x240

fwqvga
     432x240

hvga
     480x320

qhd
     960x540

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 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

Ratio
=====

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.

Color
=====

It can be the name of a color as defined below (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 or 0.0 means completely transparent, 0xff or 1.0 completely opaque). If the alpha component is not specified then 0xff is assumed.

The string random will result in a random color.

The following names of colors are recognized:

AliceBlue
     0xF0F8FF

AntiqueWhite
     0xFAEBD7

Aqua
     0x00FFFF

Aquamarine
     0x7FFFD4

Azure
     0xF0FFFF

Beige
     0xF5F5DC

Bisque
     0xFFE4C4

Black
     0x000000

BlanchedAlmond
     0xFFEBCD

Blue
     0x0000FF

BlueViolet
     0x8A2BE2

Brown
     0xA52A2A

BurlyWood
     0xDEB887

CadetBlue
     0x5F9EA0

Chartreuse
     0x7FFF00

Chocolate
     0xD2691E

Coral
     0xFF7F50

CornflowerBlue
     0x6495ED

Cornsilk
     0xFFF8DC

Crimson
     0xDC143C

Cyan
     0x00FFFF

DarkBlue
     0x00008B

DarkCyan
     0x008B8B

DarkGoldenRod
     0xB8860B

DarkGray
     0xA9A9A9

DarkGreen
     0x006400

DarkKhaki
     0xBDB76B

DarkMagenta
     0x8B008B

DarkOliveGreen
     0x556B2F

Darkorange
     0xFF8C00

DarkOrchid
     0x9932CC

DarkRed
     0x8B0000

DarkSalmon
     0xE9967A

DarkSeaGreen
     0x8FBC8F

DarkSlateBlue
     0x483D8B

DarkSlateGray
     0x2F4F4F

DarkTurquoise
     0x00CED1

DarkViolet
     0x9400D3

DeepPink
     0xFF1493

DeepSkyBlue
     0x00BFFF

DimGray
     0x696969

DodgerBlue
     0x1E90FF

FireBrick
     0xB22222

FloralWhite
     0xFFFAF0

ForestGreen
     0x228B22

Fuchsia
     0xFF00FF

Gainsboro
     0xDCDCDC

GhostWhite
     0xF8F8FF

Gold
     0xFFD700

GoldenRod
     0xDAA520

Gray
     0x808080

Green
     0x008000

GreenYellow
     0xADFF2F

HoneyDew
     0xF0FFF0

HotPink
     0xFF69B4

IndianRed
     0xCD5C5C

Indigo
     0x4B0082

Ivory
     0xFFFFF0

Khaki
     0xF0E68C

Lavender
     0xE6E6FA

LavenderBlush
     0xFFF0F5

LawnGreen
     0x7CFC00

LemonChiffon
     0xFFFACD

LightBlue
     0xADD8E6

LightCoral
     0xF08080

LightCyan
     0xE0FFFF

LightGoldenRodYellow
     0xFAFAD2

LightGreen
     0x90EE90

LightGrey
     0xD3D3D3

LightPink
     0xFFB6C1

LightSalmon
     0xFFA07A

LightSeaGreen
     0x20B2AA

LightSkyBlue
     0x87CEFA

LightSlateGray
     0x778899

LightSteelBlue
     0xB0C4DE

LightYellow
     0xFFFFE0

Lime
     0x00FF00

LimeGreen
     0x32CD32

Linen
     0xFAF0E6

Magenta
     0xFF00FF

Maroon
     0x800000

MediumAquaMarine
     0x66CDAA

MediumBlue
     0x0000CD

MediumOrchid
     0xBA55D3

MediumPurple
     0x9370D8

MediumSeaGreen
     0x3CB371

MediumSlateBlue
     0x7B68EE

MediumSpringGreen
     0x00FA9A

MediumTurquoise
     0x48D1CC

MediumVioletRed
     0xC71585

MidnightBlue
     0x191970

MintCream
     0xF5FFFA

MistyRose
     0xFFE4E1

Moccasin
     0xFFE4B5

NavajoWhite
     0xFFDEAD

Navy
     0x000080

OldLace
     0xFDF5E6

Olive
     0x808000

OliveDrab
     0x6B8E23

Orange
     0xFFA500

OrangeRed
     0xFF4500

Orchid
     0xDA70D6

PaleGoldenRod
     0xEEE8AA

PaleGreen
     0x98FB98

PaleTurquoise
     0xAFEEEE

PaleVioletRed
     0xD87093

PapayaWhip
     0xFFEFD5

PeachPuff
     0xFFDAB9

Peru
     0xCD853F

Pink
     0xFFC0CB

Plum
     0xDDA0DD

PowderBlue
     0xB0E0E6

Purple
     0x800080

Red
     0xFF0000

RosyBrown
     0xBC8F8F

RoyalBlue
     0x4169E1

SaddleBrown
     0x8B4513

Salmon
     0xFA8072

SandyBrown
     0xF4A460

SeaGreen
     0x2E8B57

SeaShell
     0xFFF5EE

Sienna
     0xA0522D

Silver
     0xC0C0C0

SkyBlue
     0x87CEEB

SlateBlue
     0x6A5ACD

SlateGray
     0x708090

Snow
     0xFFFAFA

SpringGreen
     0x00FF7F

SteelBlue
     0x4682B4

Tan
     0xD2B48C

Teal
     0x008080

Thistle
     0xD8BFD8

Tomato
     0xFF6347

Turquoise
     0x40E0D0

Violet
     0xEE82EE

Wheat
     0xF5DEB3

White
     0xFFFFFF

WhiteSmoke
     0xF5F5F5

Yellow
     0xFFFF00

YellowGreen
     0x9ACD32

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:

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

downmix
     DL+DR

A custom channel layout can be specified as a sequence of terms, separated by '+' or '|'. Each term can be:

  * the name of a standard channel layout (e.g. mono, stereo, 4.0, quad, 5.0, etc.)

  * the name of a single channel (e.g. FL, FR, FC, LFE, etc.)

  * a number of channels, in decimal, optionally followed by 'c', yielding the default channel layout for that number of channels (see the function av_get_default_channel_layout)

  * a channel layout mask, in hexadecimal starting with "0x" (see the AV_CH_* macros in libavutil/channel_layout.h.

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 av_get_channel_layout defined in libavutil/channel_layout.h.

Expression Evaluation
*********************

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.

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".

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)
     Allow to load the value of the internal variable with number VAR, which was previously stored with st(VAR, EXPR). The function returns the loaded value.

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 maximum 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.

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)
     Allow to 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

OpenCL Options
**************

When FFmpeg is configured with --enable-opencl, it is possible to set the options for the global OpenCL context.

The list of supported options follows:

build_options
     Set build options used to compile the registered kernels.

     See reference "OpenCL Specification Version: 1.2 chapter 5.6.4".

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 ffmpeg -opencl_bench or av_opencl_get_device_list().

device_idx
     Select the index of the device used to run OpenCL code.

     The specified index must be one of the indexes in the device list which can be obtained with ffmpeg -opencl_bench or av_opencl_get_device_list().