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