@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{ffmpeg -opencl_bench} or @code{av_opencl_get_device_list()}.

 
 @item 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 @code{ffmpeg -opencl_bench} or @code{av_opencl_get_device_list()}.

 
 @end table
 
 @c man end OPENCL OPTIONS