MAN page from Fedora 27 ffplay-3.4.2-1.fc27.x86_64.rpm
ffplay - FFplay media player
FFplay is a very simple and portable media player using the FFmpeglibraries and the SDL
library. It is mostly used as a testbed for thevarious FFmpeg APIs.
All the numerical options, if not specified otherwise, accept a stringrepresenting a number as input, which may be followed by one of the SI
unit prefixes, for example: 'K', 'M', or 'G'.
If 'i' is appended to the SI unit prefix, the complete prefix will beinterpreted as a unit prefix for binary multiples, which are based onpowers of 1024 instead of powers of 1000. Appending 'B' to the SI unitprefix multiplies the value by 8. This allows using, for example:'KB', 'MiB', 'G' and 'B' as number suffixes.
Options which do not take arguments are boolean options, and set thecorresponding value to true. They can be set to false by prefixingthe option name with ``no''. For example using ``-nofoo''will set the boolean option with name ``foo'' to false.
Some options are applied per-stream, e.g. bitrate or codec. Stream specifiersare used to precisely specify which stream(s) a given option belongs to.
A stream specifier is a string generally appended to the option name andseparated from it by a colon. E.g. "-codec:a:1 ac3" contains the"a:1" stream specifier, which matches the second audio stream. Therefore, itwould select the ac3 codec for the second audio stream.
A stream specifier can match several streams, so that the option is applied to allof them. E.g. the stream specifier in "-b:a 128k" matches all audiostreams.
An empty stream specifier matches all streams. For example, "-codec copy"or "-codec: copy" would copy all the streams without reencoding.
Possible forms of stream specifiers are:
- Matches the stream with this index. E.g. "-threads:1 4" would set thethread count for the second stream to 4.
- stream_type is one of following: 'v' or 'V' for video, 'a' for audio, 's'for subtitle, 'd' for data, and 't' for attachments. 'v' matches all videostreams, 'V' only matches video streams which are not attached pictures, videothumbnails or cover arts. If stream_index is given, then it matchesstream number stream_index of this type. Otherwise, it matches allstreams of this type.
- If stream_index is given, then it matches the stream with number stream_indexin the program with the id program_id. Otherwise, it matches all streams in theprogram.
- #stream_id or i:stream_id
- Match the stream by stream id (e.g. PID in MPEG-TS container).
- Matches streams with the metadata tag key having the specified value. Ifvalue is not given, matches streams that contain the given tag with anyvalue.
- Matches streams with usable configuration, the codec must be defined and theessential information such as video dimension or audio sample rate must be present.
Note that in ffmpeg, matching by metadata will only work properly forinput files.
These options are shared amongst the ff* tools.
- Show license.
- -h, -?, -help, --help [arg]
- Show help. An optional parameter may be specified to print help about a specificitem. If no argument is specified, only basic (non advanced) tooloptions are shown.
Possible values of arg are:
- Print advanced tool options in addition to the basic tool options.
- Print complete list of options, including shared and private optionsfor encoders, decoders, demuxers, muxers, filters, etc.
- Print detailed information about the decoder named decoder_name. Use the-decoders option to get a list of all decoders.
- Print detailed information about the encoder named encoder_name. Use the-encoders option to get a list of all encoders.
- Print detailed information about the demuxer named demuxer_name. Use the-formats option to get a list of all demuxers and muxers.
- Print detailed information about the muxer named muxer_name. Use the-formats option to get a list of all muxers and demuxers.
- Print detailed information about the filter name filter_name. Use the-filters option to get a list of all filters.
- Show version.
- Show available formats (including devices).
- Show available demuxers.
- Show available muxers.
- Show available devices.
- Show all codecs known to libavcodec.
Note that the term 'codec' is used throughout this documentation as a shortcutfor what is more correctly called a media bitstream format.
- Show available decoders.
- Show all available encoders.
- Show available bitstream filters.
- Show available protocols.
- Show available libavfilter filters.
- Show available pixel formats.
- Show available sample formats.
- Show channel names and standard channel layouts.
- Show recognized color names.
- -sources device[,opt1=val1[,opt2=val2]...]
- Show autodetected sources of the input device.Some devices may provide system-dependent source names that cannot be autodetected.The returned list cannot be assumed to be always complete.
ffmpeg -sources pulse,server=192.168.0.4
- -sinks device[,opt1=val1[,opt2=val2]...]
- Show autodetected sinks of the output device.Some devices may provide system-dependent sink names that cannot be autodetected.The returned list cannot be assumed to be always complete.
ffmpeg -sinks pulse,server=192.168.0.4
- -loglevel [repeat+]loglevel | -v [repeat+]loglevel
- Set the logging level used by the library.Adding ``repeat+'' indicates that repeated log output should not be compressedto the first line and the ``Last message repeated n times'' line will beomitted. ``repeat'' can also be used alone.If ``repeat'' is used alone, and with no prior loglevel set, the defaultloglevel will be used. If multiple loglevel parameters are given, using'repeat' will not change the loglevel.loglevel is a string or a number containing one of the following values:
- quiet, -8
- Show nothing at all; be silent.
- panic, 0
- Only show fatal errors which could lead the process to crash, such asan assertion failure. This is not currently used for anything.
- fatal, 8
- Only show fatal errors. These are errors after which the process absolutelycannot continue.
- error, 16
- Show all errors, including ones which can be recovered from.
- warning, 24
- Show all warnings and errors. Any message related to possiblyincorrect or unexpected events will be shown.
- info, 32
- Show informative messages during processing. This is in addition towarnings and errors. This is the default value.
- verbose, 40
- Same as "info", except more verbose.
- debug, 48
- Show everything, including debugging information.
- trace, 56
By default the program logs to stderr. If coloring is supported by theterminal, colors are used to mark errors and warnings. Log coloringcan be disabled setting the environment variableAV_LOG_FORCE_NOCOLOR or NO_COLOR, or can be forced settingthe environment variable AV_LOG_FORCE_COLOR.The use of the environment variable NO_COLOR is deprecated andwill be dropped in a future FFmpeg version.
- Dump full command line and console output to a file named"program-YYYYMMDD-HHMMSS.log" in the currentdirectory.This file can be useful for bug reports.It also implies "-loglevel verbose".
Setting the environment variable FFREPORT to any value has thesame effect. If the value is a ':'-separated key=value sequence, theseoptions will affect the report; option values must be escaped if theycontain special characters or the options delimiter ':' (see the``Quoting and escaping'' section in the ffmpeg-utils manual).
The following options are recognized:
- set the file name to use for the report; %p is expanded to the nameof the program, %t is expanded to a timestamp, "%%" is expandedto a plain "%"
- set the log verbosity level using a numerical value (see "-loglevel").
For example, to output a report to a file named ffreport.logusing a log level of 32 (alias for log level "info"):
FFREPORT=file=ffreport.log:level=32 ffmpeg -i input output
Errors in parsing the environment variable are not fatal, and will notappear in the report.
- Suppress printing banner.
All FFmpeg tools will normally show a copyright notice, build optionsand library versions. This option can be used to suppress printingthis information.
- -cpuflags flags (global)
- Allows setting and clearing cpu flags. This option is intendedfor testing. Do not use it unless you know what you're doing.
ffmpeg -cpuflags -sse+mmx ... ffmpeg -cpuflags mmx ... ffmpeg -cpuflags 0 ...
Possible flags for this option are:
- Specific Processors
- This option is used to benchmark all available OpenCL devices and print theresults. This option is only available when FFmpeg has been compiled with"--enable-opencl".
When FFmpeg is configured with "--enable-opencl", the options for theglobal OpenCL context are set via -opencl_options. See the``OpenCL Options'' section in the ffmpeg-utils manual for the complete list ofsupported options. Amongst others, these options include the ability to selecta specific platform and device to run the OpenCL code on. By default, FFmpegwill run on the first device of the first platform. While the options for theglobal OpenCL context provide flexibility to the user in selecting the OpenCLdevice of their choice, most users would probably want to select the fastestOpenCL device for their system.
This option assists the selection of the most efficient configuration byidentifying the appropriate device for the user's system. The built-inbenchmark is run on all the OpenCL devices and the performance is measured foreach device. The devices in the results list are sorted based on theirperformance with the fastest device listed first. The user can subsequentlyinvoke ffmpeg using the device deemed most appropriate via-opencl_options to obtain the best performance for the OpenCLaccelerated code.
Typical usage to use the fastest OpenCL device involve the following steps.
Run the command:
Note down the platform ID (pidx) and device ID (didx) of the firsti.e. fastest device in the list.Select the platform and device using the command:
ffmpeg -opencl_options platform_idx=<pidx>:device_idx=<didx> ...
- -opencl_options options (global)
- Set OpenCL environment options. This option is only available whenFFmpeg has been compiled with "--enable-opencl".
options must be a list of key=value option pairsseparated by ':'. See the ``OpenCL Options'' section in theffmpeg-utils manual for the list of supported options.
These options are provided directly by the libavformat, libavdevice andlibavcodec libraries. To see the list of available AVOptions, use the-help
option. They are separated into two categories:
- These options can be set for any container, codec or device. Generic optionsare listed under AVFormatContext options for containers/devices and underAVCodecContext options for codecs.
- These options are specific to the given container, device or codec. Privateoptions are listed under their corresponding containers/devices/codecs.
For example to write an ID3v2.3 header instead of a default ID3v2.4 toan MP3 file, use the id3v2_version private option of the MP3muxer:
ffmpeg -i input.flac -id3v2_version 3 out.mp3
All codec AVOptions are per-stream, and thus a stream specifiershould be attached to them.
Note: the -nooption syntax cannot be used for booleanAVOptions, use -option 0/-option 1.
Note: the old undocumented way of specifying per-stream AVOptions byprepending v/a/s to the options name is now obsolete and will beremoved soon.
- -x width
- Force displayed width.
- -y height
- Force displayed height.
- -s size
- Set frame size (WxH or abbreviation), needed for videos which donot contain a header with the frame size like raw YUV. This optionhas been deprecated in favor of private options, try -video_size.
- Start in fullscreen mode.
- Disable audio.
- Disable video.
- Disable subtitles.
- -ss pos
- Seek to pos. Note that in most formats it is not possible to seekexactly, so ffplay will seek to the nearest seek point topos.
pos must be a time duration specification,see the Time duration section in the ffmpeg-utils(1) manual.
- -t duration
- Play duration seconds of audio/video.
duration must be a time duration specification,see the Time duration section in the ffmpeg-utils(1) manual.
- Seek by bytes.
- Disable graphical display.
- Borderless window.
- Set the startup volume. 0 means silence, 100 means no volume reduction oramplification. Negative values are treated as 0, values above 100 are treatedas 100.
- -f fmt
- Force format.
- -window_title title
- Set window title (default is the input filename).
- -loop number
- Loops movie playback <number> times. 0 means forever.
- -showmode mode
- Set the show mode to use.Available values for mode are:
- 0, video
- show video
- 1, waves
- show audio waves
- 2, rdft
- show audio frequency band using RDFT ((Inverse) Real Discrete Fourier Transform)
Default value is ``video'', if video is not present or cannot be played``rdft'' is automatically selected.
You can interactively cycle through the available show modes bypressing the key w.
- -vf filtergraph
- Create the filtergraph specified by filtergraph and use it tofilter the video stream.
filtergraph is a description of the filtergraph to apply tothe stream, and must have a single video input and a single videooutput. In the filtergraph, the input is associated to the label"in", and the output to the label "out". See theffmpeg-filters manual for more information about the filtergraphsyntax.
You can specify this parameter multiple times and cycle through the specifiedfiltergraphs along with the show modes by pressing the key w.
- -af filtergraph
- filtergraph is a description of the filtergraph to apply tothe input audio.Use the option ``-filters'' to show all the available filters (includingsources and sinks).
- -i input_url
- Read input_url.
- -pix_fmt format
- Set pixel format.This option has been deprecated in favor of private options, try -pixel_format.
- Print several playback statistics, in particular show the streamduration, the codec parameters, the current position in the stream andthe audio/video synchronisation drift. It is on by default, toexplicitly disable it you need to specify "-nostats".
- Non-spec-compliant optimizations.
- Generate pts.
- -sync type
- Set the master clock to audio ("type=audio"), video("type=video") or external ("type=ext"). Default is audio. Themaster clock is used to control audio-video synchronization. Most mediaplayers use audio as master clock, but in some cases (streaming or highquality broadcast) it is necessary to change that. This option is mainlyused for debugging purposes.
- -ast audio_stream_specifier
- Select the desired audio stream using the given stream specifier. The streamspecifiers are described in the Stream specifiers chapter. If this optionis not specified, the ``best'' audio stream is selected in the program of thealready selected video stream.
- -vst video_stream_specifier
- Select the desired video stream using the given stream specifier. The streamspecifiers are described in the Stream specifiers chapter. If this optionis not specified, the ``best'' video stream is selected.
- -sst subtitle_stream_specifier
- Select the desired subtitle stream using the given stream specifier. The streamspecifiers are described in the Stream specifiers chapter. If this optionis not specified, the ``best'' subtitle stream is selected in the program of thealready selected video or audio stream.
- Exit when video is done playing.
- Exit if any key is pressed.
- Exit if any mouse button is pressed.
- -codec:media_specifier codec_name
- Force a specific decoder implementation for the stream identified bymedia_specifier, which can assume the values "a" (audio),"v" (video), and "s" subtitle.
- -acodec codec_name
- Force a specific audio decoder.
- -vcodec codec_name
- Force a specific video decoder.
- -scodec codec_name
- Force a specific subtitle decoder.
- Automatically rotate the video according to file metadata. Enabled bydefault, use -noautorotate to disable it.
- Drop video frames if video is out of sync. Enabled by default if the masterclock is not set to video. Use this option to enable frame dropping for allmaster clock sources, use -noframedrop to disable it.
- Do not limit the input buffer size, read as much data as possible from theinput as soon as possible. Enabled by default for realtime streams, where datamay be dropped if not read in time. Use this option to enable infinite buffersfor all inputs, use -noinfbuf to disable it.
- q, ESC
- Toggle full screen.
- p, SPC
- Toggle mute.
- 9, 0
- Decrease and increase volume respectively.
- /, *
- Decrease and increase volume respectively.
- Cycle audio channel in the current program.
- Cycle video channel.
- Cycle subtitle channel in the current program.
- Cycle program.
- Cycle video filters or show modes.
- Step to the next frame.
Pause if the stream is not already paused, step to the next videoframe, and pause.
- Seek backward/forward 10 seconds.
- Seek backward/forward 1 minute.
- page down/page up
- Seek to the previous/next chapter.or if there are no chaptersSeek backward/forward 10 minutes.
- right mouse click
- Seek to percentage in file corresponding to fraction of width.
- left mouse double-click
- Toggle full screen.
This section documents the syntax and formats employed by the FFmpeglibraries and tools.
Quoting and escaping
FFmpeg adopts the following quoting and escaping mechanism, unlessexplicitly specified. The following rules are applied:
- ' and \ are special characters (respectively used forquoting and escaping). In addition to them, there might be otherspecial characters depending on the specific syntax where the escapingand quoting are employed.
- A special character is escaped by prefixing it with a \.
- All characters enclosed between '' are included literally in theparsed 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, areremoved from the parsed string.
Note that you may need to add a second level of escaping when usingthe command line or a script, which depends on the syntax of theadopted shell language.
The function "av_get_token" defined inlibavutil/avstring.h can be used to parse a token quoted orescaped according to the rules defined above.
The tool tools/ffescape in the FFmpeg source tree can be usedto automatically quote or escape a string in a script.
- Escape the string "Crime d'Amour" containing the "'" specialcharacter:
- The string above contains a quote, so the "'" needs to be escapedwhen quoting it:
- 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
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 isinterpreted as UTC.If the year-month-day part is not specified it takes the currentyear-month-day.
There are two accepted syntaxes for expressing time duration.
HH expresses the number of hours, MM the number of minutesfor a maximum of 2 digits, and SS the number of seconds for amaximum of 2 digits. The m at the end expresses decimal value forSS.
S expresses the number of seconds, with the optional decimal partm.
In both expressions, the optional - indicates negative duration.
The following examples are all valid time duration:
- 55 seconds
- 12 hours, 03 minutes and 45 seconds
- 23.189 seconds
Specify the size of the sourced video, it may be a string of the formwidth
, or the name of a size abbreviation.
The following abbreviations are recognized:
Specify the frame rate of a video, expressed as the number of framesgenerated per second. It has to be a string in the formatframe_rate_num
, an integer number, a floatnumber or a valid video frame rate abbreviation.
The following abbreviations are recognized:
A ratio can be expressed as an expression, or in the formnumerator
Note that a ratio with infinite (1/0) or negative value isconsidered valid, so you should check on the returned value if youwant 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 stringrepresenting the alpha component.
The alpha component may be a string composed by ``0x'' followed by anhexadecimal number or a decimal number between 0.0 and 1.0, whichrepresents the opacity value (0x00 or 0.0 means completelytransparent, 0xff or 1.0 completely opaque). If the alphacomponent is not specified then 0xff is assumed.
The string random will result in a random color.
The following names of colors are recognized:
A channel layout specifies the spatial disposition of the channels ina multi-channel audio stream. To specify a channel layout, FFmpegmakes use of a special syntax.
Individual channels are identified by an id, as given by the tablebelow:
- front left
- front right
- front center
- low frequency
- back left
- back right
- front left-of-center
- front right-of-center
- back center
- side left
- side right
- top center
- top front left
- top front center
- top front right
- top back left
- top back center
- top back right
- downmix left
- downmix right
- wide left
- wide right
- surround direct left
- surround direct right
- low frequency 2
Standard channel layout compositions can be specified by using thefollowing identifiers:
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, followed by 'c', yielding the default channellayout for that number of channels (see the function"av_get_default_channel_layout"). Note that not all channel counts have adefault layout.
- a number of channels, in decimal, followed by 'C', yielding an unknown channellayout with the specified number of channels. Note that not all channel layoutspecification strings support unknown channel layouts.
- a channel layout mask, in hexadecimal starting with ``0x'' (see the"AV_CH_*" macros in libavutil/channel_layout.h.
Before libavutil version 53 the trailing character ``c'' to specify a number ofchannels was optional, but now it is required, while a channel layout mask canalso be specified as a decimal number (if and only if not followed by ``c'' or ``C'').
See also the function "av_get_channel_layout" defined inlibavutil/channel_layout.h.
When evaluating an arithmetic expression, FFmpeg uses an internalformula evaluator, implemented through the libavutil/eval.h
An expression may contain unary, binary operators, constants, andfunctions.
Two expressions expr1 and expr2 can be combined to formanother expression "expr1;expr2".expr1 and expr2 are evaluated in turn, and the newexpression evaluates to the value of expr2.
The following binary operators are available: "+", "-","*", "/", "^".
The following unary operators are available: "+", "-".
The following functions are available:
- Compute absolute value of x.
- Compute arccosine of x.
- Compute arcsine of x.
- Compute arctangent of x.
- atan2(x, y)
- Compute principal value of the arc tangent of y/x.
- between(x, min, max)
- Return 1 if x is greater than or equal to min and lesser than orequal 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 tointegers before executing the bitwise operation.
Note that both the conversion to integer and the conversion back tofloating point can lose precision. Beware of unexpected results forlarge numbers (usually 2^53 and larger).
- Round the value of expression expr upwards to the nearestinteger. For example, ``ceil(1.5)'' is ``2.0''.
- clip(x, min, max)
- Return the value of x clipped between min and max.
- Compute cosine of x.
- Compute hyperbolic cosine of x.
- eq(x, y)
- Return 1 if x and y are equivalent, 0 otherwise.
- Compute exponential of x (with base "e", the Euler's number).
- Round the value of expression expr downwards to the nearestinteger. For example, ``floor(-1.5)'' is ``-2.0''.
- 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 andy 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 aright triangle with sides of length x and y, or the distance of thepoint (x, y) from the origin.
- if(x, y)
- Evaluate x, and if the result is non-zero return the result ofthe evaluation of y, return 0 otherwise.
- if(x, y, z)
- Evaluate x, and if the result is non-zero return the evaluationresult of y, otherwise the evaluation result of z.
- ifnot(x, y)
- Evaluate x, and if the result is zero return the result of theevaluation of y, return 0 otherwise.
- ifnot(x, y, z)
- Evaluate x, and if the result is zero return the evaluationresult of y, otherwise the evaluation result of z.
- Return 1.0 if x is +/-INFINITY, 0.0 otherwise.
- Return 1.0 if x is NAN, 0.0 otherwise.
- Load the value of the internal variable with numbervar, which was previously stored with st(var, expr).The function returns the loaded value.
- lerp(x, y, z)
- Return linear interpolation between x and y by amount of z.
- 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 minimum between x and y.
- mod(x, y)
- Compute the remainder of division of x by y.
- 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, l)
- Print the value of expression t with loglevel l. Ifl is not specified then a default log level is used.Returns the value of the expression printed.
Prints t with loglevel l
- Return a pseudo random value between 0.0 and 1.0. x is the index of theinternal variable which will be used to save the seed/state.
- root(expr, max)
- Find an input value for which the function represented by exprwith argument ld(0) is 0 in the interval 0..max.
The expression in expr must denote a continuous function or theresult is undefined.
ld(0) is used to represent the function input value, which meansthat the given expression will be evaluated multiple times withvarious input values that the expression can access throughld(0). When the expression evaluates to 0 then thecorresponding input value will be returned.
- Round the value of expression expr to the nearest integer. For example, ``round(1.5)'' is ``2.0''.
- Compute sine of x.
- Compute hyperbolic sine of x.
- Compute the square root of expr. This is equivalent to"(expr)^.5".
- Compute expression "1/(1 + exp(4*x))".
- st(var, expr)
- Store the value of the expression expr in an internalvariable. var specifies the number of the variable where tostore the value, and it is a value ranging from 0 to 9. The functionreturns the value stored in the internal variable.Note, Variables are currently not shared between expressions.
- Compute tangent of x.
- Compute hyperbolic tangent of x.
- taylor(expr, x)
- taylor(expr, x, id)
- Evaluate a Taylor series at x, given an expression representingthe "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 timeswith 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.
- Return the current (wallclock) time in seconds.
- Round the value of expression expr towards zero to the nearestinteger. For example, ``trunc(-1.5)'' is ``-1.0''.
- while(cond, expr)
- Evaluate expression expr while the expression cond isnon-zero, and returns the value of the last expr evaluation, orNAN if cond was always false.
The following constants are available:
- area of the unit disc, approximately 3.14
- exp(1) (Euler's number), approximately 2.718
- golden ratio (1+sqrt(5))/2, approximately 1.618
Assuming that an expression is considered ``true'' if it has a non-zerovalue, note that:
"*" works like AND
"+" works like OR
For example the construct:
if (A AND B) then C
is equivalent to:
In your C code, you can extend the list of unary and binary functions,and define recognized constants, so that they are available for yourexpressions.
The evaluator also recognizes the International System unit prefixes.If 'i' is appended after the prefix, binary prefixes are used, whichare based on powers of 1024 instead of powers of 1000.The 'B' postfix multiplies the value by 8, and can be appended after aunit 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, withindication of the corresponding powers of 10 and of 2.
- 10^-24 / 2^-80
- 10^-21 / 2^-70
- 10^-18 / 2^-60
- 10^-15 / 2^-50
- 10^-12 / 2^-40
- 10^-9 / 2^-30
- 10^-6 / 2^-20
- 10^-3 / 2^-10
- 10^3 / 2^10
- 10^3 / 2^10
- 10^6 / 2^20
- 10^9 / 2^30
- 10^12 / 2^40
- 10^15 / 2^40
- 10^18 / 2^50
- 10^21 / 2^60
- 10^24 / 2^70
When FFmpeg is configured with "--enable-opencl"
, it is possibleto set the options for the global OpenCL context.
The list of supported options follows:
- Set build options used to compile the registered kernels.
See reference ``OpenCL Specification Version: 1.2 chapter 5.6.4''.
- Select the index of the platform to run OpenCL code.
The specified index must be one of the indexes in the device listwhich can be obtained with "ffmpeg -opencl_bench" or "av_opencl_get_device_list()".
- Select the index of the device used to run OpenCL code.
The specified index must be one of the indexes in the device list whichcan be obtained with "ffmpeg -opencl_bench" or "av_opencl_get_device_list()".
libavcodec provides some generic global options, which can be set onall the encoders and decoders. In addition each codec may supportso-called private options, which are specific for a given codec.
Sometimes, a global option may only affect a specific kind of codec,and may be nonsensical or ignored by another, so you need to be awareof the meaning of the specified options. Also some options aremeant only for decoding or encoding.
Options may be set by specifying -option value in theFFmpeg tools, or by setting the value explicitly in the"AVCodecContext" options or using the libavutil/opt.h APIfor programmatic use.
The list of supported options follow:
- b integer (encoding,audio,video)
- Set bitrate in bits/s. Default value is 200K.
- ab integer (encoding,audio)
- Set audio bitrate (in bits/s). Default value is 128K.
- bt integer (encoding,video)
- Set video bitrate tolerance (in bits/s). In 1-pass mode, bitratetolerance specifies how far ratecontrol is willing to deviate from thetarget average bitrate value. This is not related to min/maxbitrate. Lowering tolerance too much has an adverse effect on quality.
- flags flags (decoding/encoding,audio,video,subtitles)
- Set generic flags.
- Use four motion vector by macroblock (mpeg4).
- Use 1/4 pel motion compensation.
- Use loop filter.
- Use fixed qscale.
- Use gmc.
- Always try a mb with mv=<0,0>.
- Use internal 2pass ratecontrol in first pass mode.