1\input texinfo @c -*- texinfo -*- 2 3@settitle FFmpeg FAQ 4@titlepage 5@center @titlefont{FFmpeg FAQ} 6@end titlepage 7 8@top 9 10@contents 11 12@chapter General Questions 13 14@section Why doesn't FFmpeg support feature [xyz]? 15 16Because no one has taken on that task yet. FFmpeg development is 17driven by the tasks that are important to the individual developers. 18If there is a feature that is important to you, the best way to get 19it implemented is to undertake the task yourself or sponsor a developer. 20 21@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it? 22 23No. Windows DLLs are not portable, bloated and often slow. 24Moreover FFmpeg strives to support all codecs natively. 25A DLL loader is not conducive to that goal. 26 27@section I cannot read this file although this format seems to be supported by ffmpeg. 28 29Even if ffmpeg can read the container format, it may not support all its 30codecs. Please consult the supported codec list in the ffmpeg 31documentation. 32 33@section Which codecs are supported by Windows? 34 35Windows does not support standard formats like MPEG very well, unless you 36install some additional codecs. 37 38The following list of video codecs should work on most Windows systems: 39@table @option 40@item msmpeg4v2 41.avi/.asf 42@item msmpeg4 43.asf only 44@item wmv1 45.asf only 46@item wmv2 47.asf only 48@item mpeg4 49Only if you have some MPEG-4 codec like ffdshow or Xvid installed. 50@item mpeg1video 51.mpg only 52@end table 53Note, ASF files often have .wmv or .wma extensions in Windows. It should also 54be mentioned that Microsoft claims a patent on the ASF format, and may sue 55or threaten users who create ASF files with non-Microsoft software. It is 56strongly advised to avoid ASF where possible. 57 58The following list of audio codecs should work on most Windows systems: 59@table @option 60@item adpcm_ima_wav 61@item adpcm_ms 62@item pcm_s16le 63always 64@item libmp3lame 65If some MP3 codec like LAME is installed. 66@end table 67 68 69@chapter Compilation 70 71@section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'} 72 73This is a bug in gcc. Do not report it to us. Instead, please report it to 74the gcc developers. Note that we will not add workarounds for gcc bugs. 75 76Also note that (some of) the gcc developers believe this is not a bug or 77not a bug they should fix: 78@url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}. 79Then again, some of them do not know the difference between an undecidable 80problem and an NP-hard problem... 81 82@section I have installed this library with my distro's package manager. Why does @command{configure} not see it? 83 84Distributions usually split libraries in several packages. The main package 85contains the files necessary to run programs using the library. The 86development package contains the files necessary to build programs using the 87library. Sometimes, docs and/or data are in a separate package too. 88 89To build FFmpeg, you need to install the development package. It is usually 90called @file{libfoo-dev} or @file{libfoo-devel}. You can remove it after the 91build is finished, but be sure to keep the main package. 92 93@chapter Usage 94 95@section ffmpeg does not work; what is wrong? 96 97Try a @code{make distclean} in the ffmpeg source directory before the build. 98If this does not help see 99(@url{http://ffmpeg.org/bugreports.html}). 100 101@section How do I encode single pictures into movies? 102 103First, rename your pictures to follow a numerical sequence. 104For example, img1.jpg, img2.jpg, img3.jpg,... 105Then you may run: 106 107@example 108ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg 109@end example 110 111Notice that @samp{%d} is replaced by the image number. 112 113@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc. 114 115Use the @option{-start_number} option to declare a starting number for 116the sequence. This is useful if your sequence does not start with 117@file{img001.jpg} but is still in a numerical order. The following 118example will start with @file{img100.jpg}: 119 120@example 121ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg 122@end example 123 124If you have large number of pictures to rename, you can use the 125following command to ease the burden. The command, using the bourne 126shell syntax, symbolically links all files in the current directory 127that match @code{*jpg} to the @file{/tmp} directory in the sequence of 128@file{img001.jpg}, @file{img002.jpg} and so on. 129 130@example 131x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done 132@end example 133 134If you want to sequence them by oldest modified first, substitute 135@code{$(ls -r -t *jpg)} in place of @code{*jpg}. 136 137Then run: 138 139@example 140ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg 141@end example 142 143The same logic is used for any image format that ffmpeg reads. 144 145You can also use @command{cat} to pipe images to ffmpeg: 146 147@example 148cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg 149@end example 150 151@section How do I encode movie to single pictures? 152 153Use: 154 155@example 156ffmpeg -i movie.mpg movie%d.jpg 157@end example 158 159The @file{movie.mpg} used as input will be converted to 160@file{movie1.jpg}, @file{movie2.jpg}, etc... 161 162Instead of relying on file format self-recognition, you may also use 163@table @option 164@item -c:v ppm 165@item -c:v png 166@item -c:v mjpeg 167@end table 168to force the encoding. 169 170Applying that to the previous example: 171@example 172ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg 173@end example 174 175Beware that there is no "jpeg" codec. Use "mjpeg" instead. 176 177@section Why do I see a slight quality degradation with multithreaded MPEG* encoding? 178 179For multithreaded MPEG* encoding, the encoded slices must be independent, 180otherwise thread n would practically have to wait for n-1 to finish, so it's 181quite logical that there is a small reduction of quality. This is not a bug. 182 183@section How can I read from the standard input or write to the standard output? 184 185Use @file{-} as file name. 186 187@section -f jpeg doesn't work. 188 189Try '-f image2 test%d.jpg'. 190 191@section Why can I not change the frame rate? 192 193Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates. 194Choose a different codec with the -c:v command line option. 195 196@section How do I encode Xvid or DivX video with ffmpeg? 197 198Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4 199standard (note that there are many other coding formats that use this 200same standard). Thus, use '-c:v mpeg4' to encode in these formats. The 201default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want 202a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will 203force the fourcc 'xvid' to be stored as the video fourcc rather than the 204default. 205 206@section Which are good parameters for encoding high quality MPEG-4? 207 208'-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2', 209things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'. 210 211@section Which are good parameters for encoding high quality MPEG-1/MPEG-2? 212 213'-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2' 214but beware the '-g 100' might cause problems with some decoders. 215Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd. 216 217@section Interlaced video looks very bad when encoded with ffmpeg, what is wrong? 218 219You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced 220material, and try '-top 0/1' if the result looks really messed-up. 221 222@section How can I read DirectShow files? 223 224If you have built FFmpeg with @code{./configure --enable-avisynth} 225(only possible on MinGW/Cygwin platforms), 226then you may use any file that DirectShow can read as input. 227 228Just create an "input.avs" text file with this single line ... 229@example 230DirectShowSource("C:\path to your file\yourfile.asf") 231@end example 232... and then feed that text file to ffmpeg: 233@example 234ffmpeg -i input.avs 235@end example 236 237For ANY other help on AviSynth, please visit the 238@uref{http://www.avisynth.org/, AviSynth homepage}. 239 240@section How can I join video files? 241 242To "join" video files is quite ambiguous. The following list explains the 243different kinds of "joining" and points out how those are addressed in 244FFmpeg. To join video files may mean: 245 246@itemize 247 248@item 249To put them one after the other: this is called to @emph{concatenate} them 250(in short: concat) and is addressed 251@ref{How can I concatenate video files, in this very faq}. 252 253@item 254To put them together in the same file, to let the user choose between the 255different versions (example: different audio languages): this is called to 256@emph{multiplex} them together (in short: mux), and is done by simply 257invoking ffmpeg with several @option{-i} options. 258 259@item 260For audio, to put all channels together in a single stream (example: two 261mono streams into one stereo stream): this is sometimes called to 262@emph{merge} them, and can be done using the 263@url{http://ffmpeg.org/ffmpeg-filters.html#amerge, @code{amerge}} filter. 264 265@item 266For audio, to play one on top of the other: this is called to @emph{mix} 267them, and can be done by first merging them into a single stream and then 268using the @url{http://ffmpeg.org/ffmpeg-filters.html#pan, @code{pan}} filter to mix 269the channels at will. 270 271@item 272For video, to display both together, side by side or one on top of a part of 273the other; it can be done using the 274@url{http://ffmpeg.org/ffmpeg-filters.html#overlay, @code{overlay}} video filter. 275 276@end itemize 277 278@anchor{How can I concatenate video files} 279@section How can I concatenate video files? 280 281There are several solutions, depending on the exact circumstances. 282 283@subsection Concatenating using the concat @emph{filter} 284 285FFmpeg has a @url{http://ffmpeg.org/ffmpeg-filters.html#concat, 286@code{concat}} filter designed specifically for that, with examples in the 287documentation. This operation is recommended if you need to re-encode. 288 289@subsection Concatenating using the concat @emph{demuxer} 290 291FFmpeg has a @url{http://www.ffmpeg.org/ffmpeg-formats.html#concat, 292@code{concat}} demuxer which you can use when you want to avoid a re-encode and 293your format doesn't support file level concatenation. 294 295@subsection Concatenating using the concat @emph{protocol} (file level) 296 297FFmpeg has a @url{http://ffmpeg.org/ffmpeg-protocols.html#concat, 298@code{concat}} protocol designed specifically for that, with examples in the 299documentation. 300 301A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate 302video by merely concatenating the files containing them. 303 304Hence you may concatenate your multimedia files by first transcoding them to 305these privileged formats, then using the humble @code{cat} command (or the 306equally humble @code{copy} under Windows), and finally transcoding back to your 307format of choice. 308 309@example 310ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg 311ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg 312cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg 313ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi 314@end example 315 316Additionally, you can use the @code{concat} protocol instead of @code{cat} or 317@code{copy} which will avoid creation of a potentially huge intermediate file. 318 319@example 320ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg 321ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg 322ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg 323ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi 324@end example 325 326Note that you may need to escape the character "|" which is special for many 327shells. 328 329Another option is usage of named pipes, should your platform support it: 330 331@example 332mkfifo intermediate1.mpg 333mkfifo intermediate2.mpg 334ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null & 335ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null & 336cat intermediate1.mpg intermediate2.mpg |\ 337ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi 338@end example 339 340@subsection Concatenating using raw audio and video 341 342Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also 343allow concatenation, and the transcoding step is almost lossless. 344When using multiple yuv4mpegpipe(s), the first line needs to be discarded 345from all but the first stream. This can be accomplished by piping through 346@code{tail} as seen below. Note that when piping through @code{tail} you 347must use command grouping, @code{@{ ;@}}, to background properly. 348 349For example, let's say we want to concatenate two FLV files into an 350output.flv file: 351 352@example 353mkfifo temp1.a 354mkfifo temp1.v 355mkfifo temp2.a 356mkfifo temp2.v 357mkfifo all.a 358mkfifo all.v 359ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & 360ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & 361ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & 362@{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} & 363cat temp1.a temp2.a > all.a & 364cat temp1.v temp2.v > all.v & 365ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \ 366 -f yuv4mpegpipe -i all.v \ 367 -y output.flv 368rm temp[12].[av] all.[av] 369@end example 370 371@section Using @option{-f lavfi}, audio becomes mono for no apparent reason. 372 373Use @option{-dumpgraph -} to find out exactly where the channel layout is 374lost. 375 376Most likely, it is through @code{auto-inserted aresample}. Try to understand 377why the converting filter was needed at that place. 378 379Just before the output is a likely place, as @option{-f lavfi} currently 380only support packed S16. 381 382Then insert the correct @code{aformat} explicitly in the filtergraph, 383specifying the exact format. 384 385@example 386aformat=sample_fmts=s16:channel_layouts=stereo 387@end example 388 389@section Why does FFmpeg not see the subtitles in my VOB file? 390 391VOB and a few other formats do not have a global header that describes 392everything present in the file. Instead, applications are supposed to scan 393the file to see what it contains. Since VOB files are frequently large, only 394the beginning is scanned. If the subtitles happen only later in the file, 395they will not be initially detected. 396 397Some applications, including the @code{ffmpeg} command-line tool, can only 398work with streams that were detected during the initial scan; streams that 399are detected later are ignored. 400 401The size of the initial scan is controlled by two options: @code{probesize} 402(default ~5��Mo) and @code{analyzeduration} (default 5,000,000����s = 5��s). For 403the subtitle stream to be detected, both values must be large enough. 404 405@section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead? 406 407The @option{-sameq} option meant "same quantizer", and made sense only in a 408very limited set of cases. Unfortunately, a lot of people mistook it for 409"same quality" and used it in places where it did not make sense: it had 410roughly the expected visible effect, but achieved it in a very inefficient 411way. 412 413Each encoder has its own set of options to set the quality-vs-size balance, 414use the options for the encoder you are using to set the quality level to a 415point acceptable for your tastes. The most common options to do that are 416@option{-qscale} and @option{-qmax}, but you should peruse the documentation 417of the encoder you chose. 418 419@chapter Development 420 421@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat? 422 423Yes. Check the @file{doc/examples} directory in the source 424repository, also available online at: 425@url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}. 426 427Examples are also installed by default, usually in 428@code{$PREFIX/share/ffmpeg/examples}. 429 430Also you may read the Developers Guide of the FFmpeg documentation. Alternatively, 431examine the source code for one of the many open source projects that 432already incorporate FFmpeg at (@url{projects.html}). 433 434@section Can you support my C compiler XXX? 435 436It depends. If your compiler is C99-compliant, then patches to support 437it are likely to be welcome if they do not pollute the source code 438with @code{#ifdef}s related to the compiler. 439 440@section Is Microsoft Visual C++ supported? 441 442Yes. Please see the @uref{platform.html, Microsoft Visual C++} 443section in the FFmpeg documentation. 444 445@section Can you add automake, libtool or autoconf support? 446 447No. These tools are too bloated and they complicate the build. 448 449@section Why not rewrite FFmpeg in object-oriented C++? 450 451FFmpeg is already organized in a highly modular manner and does not need to 452be rewritten in a formal object language. Further, many of the developers 453favor straight C; it works for them. For more arguments on this matter, 454read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}. 455 456@section Why are the ffmpeg programs devoid of debugging symbols? 457 458The build process creates @command{ffmpeg_g}, @command{ffplay_g}, etc. which 459contain full debug information. Those binaries are stripped to create 460@command{ffmpeg}, @command{ffplay}, etc. If you need the debug information, use 461the *_g versions. 462 463@section I do not like the LGPL, can I contribute code under the GPL instead? 464 465Yes, as long as the code is optional and can easily and cleanly be placed 466under #if CONFIG_GPL without breaking anything. So, for example, a new codec 467or filter would be OK under GPL while a bug fix to LGPL code would not. 468 469@section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves. 470 471FFmpeg builds static libraries by default. In static libraries, dependencies 472are not handled. That has two consequences. First, you must specify the 473libraries in dependency order: @code{-lavdevice} must come before 474@code{-lavformat}, @code{-lavutil} must come after everything else, etc. 475Second, external libraries that are used in FFmpeg have to be specified too. 476 477An easy way to get the full list of required libraries in dependency order 478is to use @code{pkg-config}. 479 480@example 481c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec) 482@end example 483 484See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for 485more details. 486 487@section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available. 488 489FFmpeg is a pure C project, so to use the libraries within your C++ application 490you need to explicitly state that you are using a C library. You can do this by 491encompassing your FFmpeg includes using @code{extern "C"}. 492 493See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3} 494 495@section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope 496 497FFmpeg is a pure C project using C99 math features, in order to enable C++ 498to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS 499 500@section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat? 501 502You have to create a custom AVIOContext using @code{avio_alloc_context}, 503see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources. 504 505@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm? 506 507see @url{http://www.ffmpeg.org/~michael/} 508 509@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec? 510 511Even if peculiar since it is network oriented, RTP is a container like any 512other. You have to @emph{demux} RTP before feeding the payload to libavcodec. 513In this specific case please look at RFC 4629 to see how it should be done. 514 515@section AVStream.r_frame_rate is wrong, it is much larger than the frame rate. 516 517@code{r_frame_rate} is NOT the average frame rate, it is the smallest frame rate 518that can accurately represent all timestamps. So no, it is not 519wrong if it is larger than the average! 520For example, if you have mixed 25 and 30 fps content, then @code{r_frame_rate} 521will be 150 (it is the least common multiple). 522If you are looking for the average frame rate, see @code{AVStream.avg_frame_rate}. 523 524@section Why is @code{make fate} not running all tests? 525 526Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable 527or @code{FATE_SAMPLES} environment variable or the @code{--samples} 528@command{configure} option is set to the right path. 529 530@section Why is @code{make fate} not finding the samples? 531 532Do you happen to have a @code{~} character in the samples path to indicate a 533home directory? The value is used in ways where the shell cannot expand it, 534causing FATE to not find files. Just replace @code{~} by the full path. 535 536@bye 537