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diff --git a/doc/faq.texi b/doc/faq.texi index b400124f69..ff35c898dc 100644 --- a/doc/faq.texi +++ b/doc/faq.texi @@ -1,8 +1,9 @@ \input texinfo @c -*- texinfo -*- +@documentencoding UTF-8 -@settitle Libav FAQ +@settitle FFmpeg FAQ @titlepage -@center @titlefont{Libav FAQ} +@center @titlefont{FFmpeg FAQ} @end titlepage @top @@ -11,23 +12,23 @@ @chapter General Questions -@section Why doesn't Libav support feature [xyz]? +@section Why doesn't FFmpeg support feature [xyz]? -Because no one has taken on that task yet. Libav development is +Because no one has taken on that task yet. FFmpeg development is driven by the tasks that are important to the individual developers. If there is a feature that is important to you, the best way to get it implemented is to undertake the task yourself or sponsor a developer. -@section Libav does not support codec XXX. Can you include a Windows DLL loader to support it? +@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it? No. Windows DLLs are not portable, bloated and often slow. -Moreover Libav strives to support all codecs natively. +Moreover FFmpeg strives to support all codecs natively. A DLL loader is not conducive to that goal. -@section I cannot read this file although this format seems to be supported by avconv. +@section I cannot read this file although this format seems to be supported by ffmpeg. -Even if avconv can read the container format, it may not support all its -codecs. Please consult the supported codec list in the avconv +Even if ffmpeg can read the container format, it may not support all its +codecs. Please consult the supported codec list in the ffmpeg documentation. @section Which codecs are supported by Windows? @@ -79,8 +80,75 @@ not a bug they should fix: Then again, some of them do not know the difference between an undecidable problem and an NP-hard problem... +@section I have installed this library with my distro's package manager. Why does @command{configure} not see it? + +Distributions usually split libraries in several packages. The main package +contains the files necessary to run programs using the library. The +development package contains the files necessary to build programs using the +library. Sometimes, docs and/or data are in a separate package too. + +To build FFmpeg, you need to install the development package. It is usually +called @file{libfoo-dev} or @file{libfoo-devel}. You can remove it after the +build is finished, but be sure to keep the main package. + +@section How do I make @command{pkg-config} find my libraries? + +Somewhere along with your libraries, there is a @file{.pc} file (or several) +in a @file{pkgconfig} directory. You need to set environment variables to +point @command{pkg-config} to these files. + +If you need to @emph{add} directories to @command{pkg-config}'s search list +(typical use case: library installed separately), add it to +@code{$PKG_CONFIG_PATH}: + +@example +export PKG_CONFIG_PATH=/opt/x264/lib/pkgconfig:/opt/opus/lib/pkgconfig +@end example + +If you need to @emph{replace} @command{pkg-config}'s search list +(typical use case: cross-compiling), set it in +@code{$PKG_CONFIG_LIBDIR}: + +@example +export PKG_CONFIG_LIBDIR=/home/me/cross/usr/lib/pkgconfig:/home/me/cross/usr/local/lib/pkgconfig +@end example + +If you need to know the library's internal dependencies (typical use: static +linking), add the @code{--static} option to @command{pkg-config}: + +@example +./configure --pkg-config-flags=--static +@end example + +@section How do I use @command{pkg-config} when cross-compiling? + +The best way is to install @command{pkg-config} in your cross-compilation +environment. It will automatically use the cross-compilation libraries. + +You can also use @command{pkg-config} from the host environment by +specifying explicitly @code{--pkg-config=pkg-config} to @command{configure}. +In that case, you must point @command{pkg-config} to the correct directories +using the @code{PKG_CONFIG_LIBDIR}, as explained in the previous entry. + +As an intermediate solution, you can place in your cross-compilation +environment a script that calls the host @command{pkg-config} with +@code{PKG_CONFIG_LIBDIR} set. That script can look like that: + +@example +#!/bin/sh +PKG_CONFIG_LIBDIR=/path/to/cross/lib/pkgconfig +export PKG_CONFIG_LIBDIR +exec /usr/bin/pkg-config "$@@" +@end example + @chapter Usage +@section ffmpeg does not work; what is wrong? + +Try a @code{make distclean} in the ffmpeg source directory before the build. +If this does not help see +(@url{https://ffmpeg.org/bugreports.html}). + @section How do I encode single pictures into movies? First, rename your pictures to follow a numerical sequence. @@ -88,12 +156,21 @@ For example, img1.jpg, img2.jpg, img3.jpg,... Then you may run: @example - avconv -f image2 -i img%d.jpg /tmp/a.mpg +ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg @end example Notice that @samp{%d} is replaced by the image number. -@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc... +@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc. + +Use the @option{-start_number} option to declare a starting number for +the sequence. This is useful if your sequence does not start with +@file{img001.jpg} but is still in a numerical order. The following +example will start with @file{img100.jpg}: + +@example +ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg +@end example If you have large number of pictures to rename, you can use the following command to ease the burden. The command, using the bourne @@ -102,7 +179,7 @@ that match @code{*jpg} to the @file{/tmp} directory in the sequence of @file{img001.jpg}, @file{img002.jpg} and so on. @example - x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done +x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done @end example If you want to sequence them by oldest modified first, substitute @@ -111,17 +188,23 @@ If you want to sequence them by oldest modified first, substitute Then run: @example - avconv -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg +ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg @end example -The same logic is used for any image format that avconv reads. +The same logic is used for any image format that ffmpeg reads. + +You can also use @command{cat} to pipe images to ffmpeg: + +@example +cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg +@end example @section How do I encode movie to single pictures? Use: @example - avconv -i movie.mpg movie%d.jpg +ffmpeg -i movie.mpg movie%d.jpg @end example The @file{movie.mpg} used as input will be converted to @@ -137,7 +220,7 @@ to force the encoding. Applying that to the previous example: @example - avconv -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg +ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg @end example Beware that there is no "jpeg" codec. Use "mjpeg" instead. @@ -156,12 +239,12 @@ Use @file{-} as file name. Try '-f image2 test%d.jpg'. -@section Why can I not change the framerate? +@section Why can I not change the frame rate? -Some codecs, like MPEG-1/2, only allow a small number of fixed framerates. +Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates. Choose a different codec with the -c:v command line option. -@section How do I encode Xvid or DivX video with avconv? +@section How do I encode Xvid or DivX video with ffmpeg? Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4 standard (note that there are many other coding formats that use this @@ -182,24 +265,24 @@ things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'. but beware the '-g 100' might cause problems with some decoders. Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd. -@section Interlaced video looks very bad when encoded with avconv, what is wrong? +@section Interlaced video looks very bad when encoded with ffmpeg, what is wrong? You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced material, and try '-top 0/1' if the result looks really messed-up. @section How can I read DirectShow files? -If you have built Libav with @code{./configure --enable-avisynth} +If you have built FFmpeg with @code{./configure --enable-avisynth} (only possible on MinGW/Cygwin platforms), then you may use any file that DirectShow can read as input. Just create an "input.avs" text file with this single line ... @example - DirectShowSource("C:\path to your file\yourfile.asf") +DirectShowSource("C:\path to your file\yourfile.asf") @end example -... and then feed that text file to avconv: +... and then feed that text file to ffmpeg: @example - avconv -i input.avs +ffmpeg -i input.avs @end example For ANY other help on AviSynth, please visit the @@ -207,8 +290,67 @@ For ANY other help on AviSynth, please visit the @section How can I join video files? -A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by -merely concatenating them. +To "join" video files is quite ambiguous. The following list explains the +different kinds of "joining" and points out how those are addressed in +FFmpeg. To join video files may mean: + +@itemize + +@item +To put them one after the other: this is called to @emph{concatenate} them +(in short: concat) and is addressed +@ref{How can I concatenate video files, in this very faq}. + +@item +To put them together in the same file, to let the user choose between the +different versions (example: different audio languages): this is called to +@emph{multiplex} them together (in short: mux), and is done by simply +invoking ffmpeg with several @option{-i} options. + +@item +For audio, to put all channels together in a single stream (example: two +mono streams into one stereo stream): this is sometimes called to +@emph{merge} them, and can be done using the +@url{ffmpeg-filters.html#amerge, @code{amerge}} filter. + +@item +For audio, to play one on top of the other: this is called to @emph{mix} +them, and can be done by first merging them into a single stream and then +using the @url{ffmpeg-filters.html#pan, @code{pan}} filter to mix +the channels at will. + +@item +For video, to display both together, side by side or one on top of a part of +the other; it can be done using the +@url{ffmpeg-filters.html#overlay, @code{overlay}} video filter. + +@end itemize + +@anchor{How can I concatenate video files} +@section How can I concatenate video files? + +There are several solutions, depending on the exact circumstances. + +@subsection Concatenating using the concat @emph{filter} + +FFmpeg has a @url{ffmpeg-filters.html#concat, +@code{concat}} filter designed specifically for that, with examples in the +documentation. This operation is recommended if you need to re-encode. + +@subsection Concatenating using the concat @emph{demuxer} + +FFmpeg has a @url{ffmpeg-formats.html#concat, +@code{concat}} demuxer which you can use when you want to avoid a re-encode and +your format doesn't support file level concatenation. + +@subsection Concatenating using the concat @emph{protocol} (file level) + +FFmpeg has a @url{ffmpeg-protocols.html#concat, +@code{concat}} protocol designed specifically for that, with examples in the +documentation. + +A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow one to concatenate +video by merely concatenating the files containing them. Hence you may concatenate your multimedia files by first transcoding them to these privileged formats, then using the humble @code{cat} command (or the @@ -216,27 +358,38 @@ equally humble @code{copy} under Windows), and finally transcoding back to your format of choice. @example -avconv -i input1.avi intermediate1.mpg -avconv -i input2.avi intermediate2.mpg +ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg +ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg -avconv -i intermediate_all.mpg output.avi +ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi @end example -Notice that you should set a reasonably high bitrate for your intermediate and -output files, if you want to preserve video quality. +Additionally, you can use the @code{concat} protocol instead of @code{cat} or +@code{copy} which will avoid creation of a potentially huge intermediate file. -Also notice that you may avoid the huge intermediate files by taking advantage -of named pipes, should your platform support it: +@example +ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg +ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg +ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg +ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi +@end example + +Note that you may need to escape the character "|" which is special for many +shells. + +Another option is usage of named pipes, should your platform support it: @example mkfifo intermediate1.mpg mkfifo intermediate2.mpg -avconv -i input1.avi -y intermediate1.mpg < /dev/null & -avconv -i input2.avi -y intermediate2.mpg < /dev/null & +ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null & +ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null & cat intermediate1.mpg intermediate2.mpg |\ -avconv -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi +ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi @end example +@subsection Concatenating using raw audio and video + Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also allow concatenation, and the transcoding step is almost lossless. When using multiple yuv4mpegpipe(s), the first line needs to be discarded @@ -244,7 +397,8 @@ from all but the first stream. This can be accomplished by piping through @code{tail} as seen below. Note that when piping through @code{tail} you must use command grouping, @code{@{ ;@}}, to background properly. -For example, let's say we want to join two FLV files into an output.flv file: +For example, let's say we want to concatenate two FLV files into an +output.flv file: @example mkfifo temp1.a @@ -253,45 +407,114 @@ mkfifo temp2.a mkfifo temp2.v mkfifo all.a mkfifo all.v -avconv -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & -avconv -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & -avconv -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & -@{ avconv -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} & +ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & +ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & +ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & +@{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} & cat temp1.a temp2.a > all.a & cat temp1.v temp2.v > all.v & -avconv -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \ +ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \ -f yuv4mpegpipe -i all.v \ -y output.flv rm temp[12].[av] all.[av] @end example -@section -profile option fails when encoding H.264 video with AAC audio +@section Using @option{-f lavfi}, audio becomes mono for no apparent reason. + +Use @option{-dumpgraph -} to find out exactly where the channel layout is +lost. -@command{avconv} prints an error like +Most likely, it is through @code{auto-inserted aresample}. Try to understand +why the converting filter was needed at that place. + +Just before the output is a likely place, as @option{-f lavfi} currently +only support packed S16. + +Then insert the correct @code{aformat} explicitly in the filtergraph, +specifying the exact format. @example -Undefined constant or missing '(' in 'baseline' -Unable to parse option value "baseline" -Error setting option profile to value baseline. +aformat=sample_fmts=s16:channel_layouts=stereo @end example -Short answer: write @option{-profile:v} instead of @option{-profile}. +@section Why does FFmpeg not see the subtitles in my VOB file? + +VOB and a few other formats do not have a global header that describes +everything present in the file. Instead, applications are supposed to scan +the file to see what it contains. Since VOB files are frequently large, only +the beginning is scanned. If the subtitles happen only later in the file, +they will not be initially detected. + +Some applications, including the @code{ffmpeg} command-line tool, can only +work with streams that were detected during the initial scan; streams that +are detected later are ignored. + +The size of the initial scan is controlled by two options: @code{probesize} +(default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For +the subtitle stream to be detected, both values must be large enough. + +@section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead? + +The @option{-sameq} option meant "same quantizer", and made sense only in a +very limited set of cases. Unfortunately, a lot of people mistook it for +"same quality" and used it in places where it did not make sense: it had +roughly the expected visible effect, but achieved it in a very inefficient +way. + +Each encoder has its own set of options to set the quality-vs-size balance, +use the options for the encoder you are using to set the quality level to a +point acceptable for your tastes. The most common options to do that are +@option{-qscale} and @option{-qmax}, but you should peruse the documentation +of the encoder you chose. + +@section I have a stretched video, why does scaling does not fix it? + +A lot of video codecs and formats can store the @emph{aspect ratio} of the +video: this is the ratio between the width and the height of either the full +image (DAR, display aspect ratio) or individual pixels (SAR, sample aspect +ratio). For example, EGA screens at resolution 640×350 had 4:3 DAR and 35:48 +SAR. + +Most still image processing work with square pixels, i.e. 1:1 SAR, but a lot +of video standards, especially from the analogic-numeric transition era, use +non-square pixels. -Long answer: this happens because the @option{-profile} option can apply to both -video and audio. Specifically the AAC encoder also defines some profiles, none -of which are named @var{baseline}. +Most processing filters in FFmpeg handle the aspect ratio to avoid +stretching the image: cropping adjusts the DAR to keep the SAR constant, +scaling adjusts the SAR to keep the DAR constant. -The solution is to apply the @option{-profile} option to the video stream only -by using @url{http://libav.org/avconv.html#Stream-specifiers-1, Stream specifiers}. -Appending @code{:v} to it will do exactly that. +If you want to stretch, or “unstretch”, the image, you need to override the +information with the +@url{ffmpeg-filters.html#setdar_002c-setsar, @code{setdar or setsar filters}}. + +Do not forget to examine carefully the original video to check whether the +stretching comes from the image or from the aspect ratio information. + +For example, to fix a badly encoded EGA capture, use the following commands, +either the first one to upscale to square pixels or the second one to set +the correct aspect ratio or the third one to avoid transcoding (may not work +depending on the format / codec / player / phase of the moon): + +@example +ffmpeg -i ega_screen.nut -vf scale=640:480,setsar=1 ega_screen_scaled.nut +ffmpeg -i ega_screen.nut -vf setdar=4/3 ega_screen_anamorphic.nut +ffmpeg -i ega_screen.nut -aspect 4/3 -c copy ega_screen_overridden.nut +@end example @chapter Development -@section Are there examples illustrating how to use the Libav libraries, particularly libavcodec and libavformat? +@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat? + +Yes. Check the @file{doc/examples} directory in the source +repository, also available online at: +@url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}. -Yes. Read the Developers Guide of the Libav documentation. Alternatively, +Examples are also installed by default, usually in +@code{$PREFIX/share/ffmpeg/examples}. + +Also you may read the Developers Guide of the FFmpeg documentation. Alternatively, examine the source code for one of the many open source projects that -already incorporate Libav at (@url{projects.html}). +already incorporate FFmpeg at (@url{projects.html}). @section Can you support my C compiler XXX? @@ -302,42 +525,86 @@ with @code{#ifdef}s related to the compiler. @section Is Microsoft Visual C++ supported? Yes. Please see the @uref{platform.html, Microsoft Visual C++} -section in the Libav documentation. +section in the FFmpeg documentation. @section Can you add automake, libtool or autoconf support? No. These tools are too bloated and they complicate the build. -@section Why not rewrite Libav in object-oriented C++? +@section Why not rewrite FFmpeg in object-oriented C++? -Libav is already organized in a highly modular manner and does not need to +FFmpeg is already organized in a highly modular manner and does not need to be rewritten in a formal object language. Further, many of the developers favor straight C; it works for them. For more arguments on this matter, read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}. +@section Why are the ffmpeg programs devoid of debugging symbols? + +The build process creates @command{ffmpeg_g}, @command{ffplay_g}, etc. which +contain full debug information. Those binaries are stripped to create +@command{ffmpeg}, @command{ffplay}, etc. If you need the debug information, use +the *_g versions. + @section I do not like the LGPL, can I contribute code under the GPL instead? Yes, as long as the code is optional and can easily and cleanly be placed -under #if CONFIG_GPL without breaking anything. So for example a new codec +under #if CONFIG_GPL without breaking anything. So, for example, a new codec or filter would be OK under GPL while a bug fix to LGPL code would not. -@section I'm using Libav from within my C++ application but the linker complains about missing symbols which seem to be available. +@section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves. + +FFmpeg builds static libraries by default. In static libraries, dependencies +are not handled. That has two consequences. First, you must specify the +libraries in dependency order: @code{-lavdevice} must come before +@code{-lavformat}, @code{-lavutil} must come after everything else, etc. +Second, external libraries that are used in FFmpeg have to be specified too. + +An easy way to get the full list of required libraries in dependency order +is to use @code{pkg-config}. -Libav is a pure C project, so to use the libraries within your C++ application +@example +c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec) +@end example + +See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for +more details. + +@section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available. + +FFmpeg is a pure C project, so to use the libraries within your C++ application you need to explicitly state that you are using a C library. You can do this by -encompassing your Libav includes using @code{extern "C"}. +encompassing your FFmpeg includes using @code{extern "C"}. See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3} @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope -Libav is a pure C project using C99 math features, in order to enable C++ +FFmpeg is a pure C project using C99 math features, in order to enable C++ to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat? You have to create a custom AVIOContext using @code{avio_alloc_context}, -see @file{libavformat/aviobuf.c} in Libav and @file{libmpdemux/demux_lavf.c} in MPlayer2 sources. +see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources. + +@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm? + +see @url{https://www.ffmpeg.org/~michael/} + +@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec? + +Even if peculiar since it is network oriented, RTP is a container like any +other. You have to @emph{demux} RTP before feeding the payload to libavcodec. +In this specific case please look at RFC 4629 to see how it should be done. + +@section AVStream.r_frame_rate is wrong, it is much larger than the frame rate. + +@code{r_frame_rate} is NOT the average frame rate, it is the smallest frame rate +that can accurately represent all timestamps. So no, it is not +wrong if it is larger than the average! +For example, if you have mixed 25 and 30 fps content, then @code{r_frame_rate} +will be 150 (it is the least common multiple). +If you are looking for the average frame rate, see @code{AVStream.avg_frame_rate}. @section Why is @code{make fate} not running all tests? |