FFmpeg Utilities Documentation

Table of Contents

1 Description

This document describes some generic features and utilities provided by the libavutil library.

2 Syntax

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

2.1 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.

2.1.1 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
    

2.2 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.

2.3 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.

2.3.1 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

2.4 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

2.5 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

2.6 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.

2.7 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

2.8 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.

3 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".

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)

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

4 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().

5 See Also

ffmpeg, ffplay, ffprobe, ffserver, libavutil

6 Authors

The FFmpeg developers.

For details about the authorship, see the Git history of the project (git://source.ffmpeg.org/ffmpeg), e.g. by typing the command git log in the FFmpeg source directory, or browsing the online repository at http://source.ffmpeg.org.

Maintainers for the specific components are listed in the file MAINTAINERS in the source code tree.

This document was generated on September 30, 2014 using makeinfo.