

o  ’ 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. 
o  A special character is escaped by prefixing it with a \. 
o  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. 
o  Leading and trailing whitespaces, unless escaped or quoted, are removed from the parsed string. 
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
o 
Escape the string Crime dAmour containing the special
character:
Crime d\Amour 
o 
The string above contains a quote, so the needs to be escaped
when quoting it:
Crime d\Amour 
o 
Include leading or trailing whitespaces using quoting:
this string starts and ends with whitespaces 
o 
Escaping and quoting can be mixed together:
The string \string\ is a string 
o 
To include a literal \ you can use either escaping or quoting:
c:\foo can be written as c:\\foo 
The accepted syntax is:
[(YYYYMMDDYYYYMMDD)[Tt ]]((HH:MM:SS[.m...]]])(HHMMSS[.m...]]]))[Z] nowIf 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 yearmonthday part is not specified it takes the current yearmonthday.
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
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 ntscfilm 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 2kdci 2048x1080 4kdci 4096x2160 uhd2160 3840x2160 uhd4320 7680x4320
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 ntscfilm 24000/1001
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.
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
A channel layout specifies the spatial disposition of the channels in a multichannel 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:
Standard channel layout compositions can be specified by using the following identifiers:
FL front left FR front right FC front center LFE low frequency BL back left BR back right FLC front leftofcenter FRC front rightofcenter 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 A custom channel layout can be specified as a sequence of terms, separated by ’+’ or ’’. Each term can be:
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(wideside) FL+FR+FC+LFE+FLC+FRC+SL+SR octagonal FL+FR+FC+BL+BR+BC+SL+SR downmix DL+DR 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).
o the name of a standard channel layout (e.g. mono, stereo, 4.0, quad, 5.0, etc.) o the name of a single channel (e.g. FL, FR, FC, LFE, etc.) o 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) o a channel layout mask, in hexadecimal starting with 0x (see the AV_CH_* macros in libavutil/channel_layout.h. See also the function av_get_channel_layout defined in libavutil/channel_layout.h.
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:
The following constants 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 nonzero return the result of the evaluation of y, return 0 otherwise. if(x, y, z) Evaluate x, and if the result is nonzero 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) 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) 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, xy) 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 nonzero, and returns the value of the last expr evaluation, or NAN if cond was always false. Assuming that an expression is considered true if it has a nonzero value, note that:
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 * works like AND
+ works like OR
For example the construct:
if (A AND B) then Cis 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
When FFmpeg is configured with enableopencl, 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().
ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libavutil(3)
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.
FFMPEGUTILS (1) 
Visit the GSP FreeBSD Man Page Interface.
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