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| 1 | \input texinfo @c -*- texinfo -*- |
| 2 | @documentencoding UTF-8 |
| 3 | |
| 4 | @settitle FFmpeg FAQ |
| 5 | @titlepage |
| 6 | @center @titlefont{FFmpeg FAQ} |
| 7 | @end titlepage |
| 8 | |
| 9 | @top |
| 10 | |
| 11 | @contents |
| 12 | |
| 13 | @chapter General Questions |
| 14 | |
| 15 | @section Why doesn't FFmpeg support feature [xyz]? |
| 16 | |
| 17 | Because no one has taken on that task yet. FFmpeg development is |
| 18 | driven by the tasks that are important to the individual developers. |
| 19 | If there is a feature that is important to you, the best way to get |
| 20 | it implemented is to undertake the task yourself or sponsor a developer. |
| 21 | |
| 22 | @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it? |
| 23 | |
| 24 | No. Windows DLLs are not portable, bloated and often slow. |
| 25 | Moreover FFmpeg strives to support all codecs natively. |
| 26 | A DLL loader is not conducive to that goal. |
| 27 | |
| 28 | @section I cannot read this file although this format seems to be supported by ffmpeg. |
| 29 | |
| 30 | Even if ffmpeg can read the container format, it may not support all its |
| 31 | codecs. Please consult the supported codec list in the ffmpeg |
| 32 | documentation. |
| 33 | |
| 34 | @section Which codecs are supported by Windows? |
| 35 | |
| 36 | Windows does not support standard formats like MPEG very well, unless you |
| 37 | install some additional codecs. |
| 38 | |
| 39 | The following list of video codecs should work on most Windows systems: |
| 40 | @table @option |
| 41 | @item msmpeg4v2 |
| 42 | .avi/.asf |
| 43 | @item msmpeg4 |
| 44 | .asf only |
| 45 | @item wmv1 |
| 46 | .asf only |
| 47 | @item wmv2 |
| 48 | .asf only |
| 49 | @item mpeg4 |
| 50 | Only if you have some MPEG-4 codec like ffdshow or Xvid installed. |
| 51 | @item mpeg1video |
| 52 | .mpg only |
| 53 | @end table |
| 54 | Note, ASF files often have .wmv or .wma extensions in Windows. It should also |
| 55 | be mentioned that Microsoft claims a patent on the ASF format, and may sue |
| 56 | or threaten users who create ASF files with non-Microsoft software. It is |
| 57 | strongly advised to avoid ASF where possible. |
| 58 | |
| 59 | The following list of audio codecs should work on most Windows systems: |
| 60 | @table @option |
| 61 | @item adpcm_ima_wav |
| 62 | @item adpcm_ms |
| 63 | @item pcm_s16le |
| 64 | always |
| 65 | @item libmp3lame |
| 66 | If some MP3 codec like LAME is installed. |
| 67 | @end table |
| 68 | |
| 69 | |
| 70 | @chapter Compilation |
| 71 | |
| 72 | @section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'} |
| 73 | |
| 74 | This is a bug in gcc. Do not report it to us. Instead, please report it to |
| 75 | the gcc developers. Note that we will not add workarounds for gcc bugs. |
| 76 | |
| 77 | Also note that (some of) the gcc developers believe this is not a bug or |
| 78 | not a bug they should fix: |
| 79 | @url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}. |
| 80 | Then again, some of them do not know the difference between an undecidable |
| 81 | problem and an NP-hard problem... |
| 82 | |
| 83 | @section I have installed this library with my distro's package manager. Why does @command{configure} not see it? |
| 84 | |
| 85 | Distributions usually split libraries in several packages. The main package |
| 86 | contains the files necessary to run programs using the library. The |
| 87 | development package contains the files necessary to build programs using the |
| 88 | library. Sometimes, docs and/or data are in a separate package too. |
| 89 | |
| 90 | To build FFmpeg, you need to install the development package. It is usually |
| 91 | called @file{libfoo-dev} or @file{libfoo-devel}. You can remove it after the |
| 92 | build is finished, but be sure to keep the main package. |
| 93 | |
| 94 | @section How do I make @command{pkg-config} find my libraries? |
| 95 | |
| 96 | Somewhere along with your libraries, there is a @file{.pc} file (or several) |
| 97 | in a @file{pkgconfig} directory. You need to set environment variables to |
| 98 | point @command{pkg-config} to these files. |
| 99 | |
| 100 | If you need to @emph{add} directories to @command{pkg-config}'s search list |
| 101 | (typical use case: library installed separately), add it to |
| 102 | @code{$PKG_CONFIG_PATH}: |
| 103 | |
| 104 | @example |
| 105 | export PKG_CONFIG_PATH=/opt/x264/lib/pkgconfig:/opt/opus/lib/pkgconfig |
| 106 | @end example |
| 107 | |
| 108 | If you need to @emph{replace} @command{pkg-config}'s search list |
| 109 | (typical use case: cross-compiling), set it in |
| 110 | @code{$PKG_CONFIG_LIBDIR}: |
| 111 | |
| 112 | @example |
| 113 | export PKG_CONFIG_LIBDIR=/home/me/cross/usr/lib/pkgconfig:/home/me/cross/usr/local/lib/pkgconfig |
| 114 | @end example |
| 115 | |
| 116 | If you need to know the library's internal dependencies (typical use: static |
| 117 | linking), add the @code{--static} option to @command{pkg-config}: |
| 118 | |
| 119 | @example |
| 120 | ./configure --pkg-config-flags=--static |
| 121 | @end example |
| 122 | |
| 123 | @section How do I use @command{pkg-config} when cross-compiling? |
| 124 | |
| 125 | The best way is to install @command{pkg-config} in your cross-compilation |
| 126 | environment. It will automatically use the cross-compilation libraries. |
| 127 | |
| 128 | You can also use @command{pkg-config} from the host environment by |
| 129 | specifying explicitly @code{--pkg-config=pkg-config} to @command{configure}. |
| 130 | In that case, you must point @command{pkg-config} to the correct directories |
| 131 | using the @code{PKG_CONFIG_LIBDIR}, as explained in the previous entry. |
| 132 | |
| 133 | As an intermediate solution, you can place in your cross-compilation |
| 134 | environment a script that calls the host @command{pkg-config} with |
| 135 | @code{PKG_CONFIG_LIBDIR} set. That script can look like that: |
| 136 | |
| 137 | @example |
| 138 | #!/bin/sh |
| 139 | PKG_CONFIG_LIBDIR=/path/to/cross/lib/pkgconfig |
| 140 | export PKG_CONFIG_LIBDIR |
| 141 | exec /usr/bin/pkg-config "$@@" |
| 142 | @end example |
| 143 | |
| 144 | @chapter Usage |
| 145 | |
| 146 | @section ffmpeg does not work; what is wrong? |
| 147 | |
| 148 | Try a @code{make distclean} in the ffmpeg source directory before the build. |
| 149 | If this does not help see |
| 150 | (@url{https://ffmpeg.org/bugreports.html}). |
| 151 | |
| 152 | @section How do I encode single pictures into movies? |
| 153 | |
| 154 | First, rename your pictures to follow a numerical sequence. |
| 155 | For example, img1.jpg, img2.jpg, img3.jpg,... |
| 156 | Then you may run: |
| 157 | |
| 158 | @example |
| 159 | ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg |
| 160 | @end example |
| 161 | |
| 162 | Notice that @samp{%d} is replaced by the image number. |
| 163 | |
| 164 | @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc. |
| 165 | |
| 166 | Use the @option{-start_number} option to declare a starting number for |
| 167 | the sequence. This is useful if your sequence does not start with |
| 168 | @file{img001.jpg} but is still in a numerical order. The following |
| 169 | example will start with @file{img100.jpg}: |
| 170 | |
| 171 | @example |
| 172 | ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg |
| 173 | @end example |
| 174 | |
| 175 | If you have large number of pictures to rename, you can use the |
| 176 | following command to ease the burden. The command, using the bourne |
| 177 | shell syntax, symbolically links all files in the current directory |
| 178 | that match @code{*jpg} to the @file{/tmp} directory in the sequence of |
| 179 | @file{img001.jpg}, @file{img002.jpg} and so on. |
| 180 | |
| 181 | @example |
| 182 | x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done |
| 183 | @end example |
| 184 | |
| 185 | If you want to sequence them by oldest modified first, substitute |
| 186 | @code{$(ls -r -t *jpg)} in place of @code{*jpg}. |
| 187 | |
| 188 | Then run: |
| 189 | |
| 190 | @example |
| 191 | ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg |
| 192 | @end example |
| 193 | |
| 194 | The same logic is used for any image format that ffmpeg reads. |
| 195 | |
| 196 | You can also use @command{cat} to pipe images to ffmpeg: |
| 197 | |
| 198 | @example |
| 199 | cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg |
| 200 | @end example |
| 201 | |
| 202 | @section How do I encode movie to single pictures? |
| 203 | |
| 204 | Use: |
| 205 | |
| 206 | @example |
| 207 | ffmpeg -i movie.mpg movie%d.jpg |
| 208 | @end example |
| 209 | |
| 210 | The @file{movie.mpg} used as input will be converted to |
| 211 | @file{movie1.jpg}, @file{movie2.jpg}, etc... |
| 212 | |
| 213 | Instead of relying on file format self-recognition, you may also use |
| 214 | @table @option |
| 215 | @item -c:v ppm |
| 216 | @item -c:v png |
| 217 | @item -c:v mjpeg |
| 218 | @end table |
| 219 | to force the encoding. |
| 220 | |
| 221 | Applying that to the previous example: |
| 222 | @example |
| 223 | ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg |
| 224 | @end example |
| 225 | |
| 226 | Beware that there is no "jpeg" codec. Use "mjpeg" instead. |
| 227 | |
| 228 | @section Why do I see a slight quality degradation with multithreaded MPEG* encoding? |
| 229 | |
| 230 | For multithreaded MPEG* encoding, the encoded slices must be independent, |
| 231 | otherwise thread n would practically have to wait for n-1 to finish, so it's |
| 232 | quite logical that there is a small reduction of quality. This is not a bug. |
| 233 | |
| 234 | @section How can I read from the standard input or write to the standard output? |
| 235 | |
| 236 | Use @file{-} as file name. |
| 237 | |
| 238 | @section -f jpeg doesn't work. |
| 239 | |
| 240 | Try '-f image2 test%d.jpg'. |
| 241 | |
| 242 | @section Why can I not change the frame rate? |
| 243 | |
| 244 | Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates. |
| 245 | Choose a different codec with the -c:v command line option. |
| 246 | |
| 247 | @section How do I encode Xvid or DivX video with ffmpeg? |
| 248 | |
| 249 | Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4 |
| 250 | standard (note that there are many other coding formats that use this |
| 251 | same standard). Thus, use '-c:v mpeg4' to encode in these formats. The |
| 252 | default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want |
| 253 | a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will |
| 254 | force the fourcc 'xvid' to be stored as the video fourcc rather than the |
| 255 | default. |
| 256 | |
| 257 | @section Which are good parameters for encoding high quality MPEG-4? |
| 258 | |
| 259 | '-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2', |
| 260 | things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'. |
| 261 | |
| 262 | @section Which are good parameters for encoding high quality MPEG-1/MPEG-2? |
| 263 | |
| 264 | '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2' |
| 265 | but beware the '-g 100' might cause problems with some decoders. |
| 266 | Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd. |
| 267 | |
| 268 | @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong? |
| 269 | |
| 270 | You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced |
| 271 | material, and try '-top 0/1' if the result looks really messed-up. |
| 272 | |
| 273 | @section How can I read DirectShow files? |
| 274 | |
| 275 | If you have built FFmpeg with @code{./configure --enable-avisynth} |
| 276 | (only possible on MinGW/Cygwin platforms), |
| 277 | then you may use any file that DirectShow can read as input. |
| 278 | |
| 279 | Just create an "input.avs" text file with this single line ... |
| 280 | @example |
| 281 | DirectShowSource("C:\path to your file\yourfile.asf") |
| 282 | @end example |
| 283 | ... and then feed that text file to ffmpeg: |
| 284 | @example |
| 285 | ffmpeg -i input.avs |
| 286 | @end example |
| 287 | |
| 288 | For ANY other help on AviSynth, please visit the |
| 289 | @uref{http://www.avisynth.org/, AviSynth homepage}. |
| 290 | |
| 291 | @section How can I join video files? |
| 292 | |
| 293 | To "join" video files is quite ambiguous. The following list explains the |
| 294 | different kinds of "joining" and points out how those are addressed in |
| 295 | FFmpeg. To join video files may mean: |
| 296 | |
| 297 | @itemize |
| 298 | |
| 299 | @item |
| 300 | To put them one after the other: this is called to @emph{concatenate} them |
| 301 | (in short: concat) and is addressed |
| 302 | @ref{How can I concatenate video files, in this very faq}. |
| 303 | |
| 304 | @item |
| 305 | To put them together in the same file, to let the user choose between the |
| 306 | different versions (example: different audio languages): this is called to |
| 307 | @emph{multiplex} them together (in short: mux), and is done by simply |
| 308 | invoking ffmpeg with several @option{-i} options. |
| 309 | |
| 310 | @item |
| 311 | For audio, to put all channels together in a single stream (example: two |
| 312 | mono streams into one stereo stream): this is sometimes called to |
| 313 | @emph{merge} them, and can be done using the |
| 314 | @url{ffmpeg-filters.html#amerge, @code{amerge}} filter. |
| 315 | |
| 316 | @item |
| 317 | For audio, to play one on top of the other: this is called to @emph{mix} |
| 318 | them, and can be done by first merging them into a single stream and then |
| 319 | using the @url{ffmpeg-filters.html#pan, @code{pan}} filter to mix |
| 320 | the channels at will. |
| 321 | |
| 322 | @item |
| 323 | For video, to display both together, side by side or one on top of a part of |
| 324 | the other; it can be done using the |
| 325 | @url{ffmpeg-filters.html#overlay, @code{overlay}} video filter. |
| 326 | |
| 327 | @end itemize |
| 328 | |
| 329 | @anchor{How can I concatenate video files} |
| 330 | @section How can I concatenate video files? |
| 331 | |
| 332 | There are several solutions, depending on the exact circumstances. |
| 333 | |
| 334 | @subsection Concatenating using the concat @emph{filter} |
| 335 | |
| 336 | FFmpeg has a @url{ffmpeg-filters.html#concat, |
| 337 | @code{concat}} filter designed specifically for that, with examples in the |
| 338 | documentation. This operation is recommended if you need to re-encode. |
| 339 | |
| 340 | @subsection Concatenating using the concat @emph{demuxer} |
| 341 | |
| 342 | FFmpeg has a @url{ffmpeg-formats.html#concat, |
| 343 | @code{concat}} demuxer which you can use when you want to avoid a re-encode and |
| 344 | your format doesn't support file level concatenation. |
| 345 | |
| 346 | @subsection Concatenating using the concat @emph{protocol} (file level) |
| 347 | |
| 348 | FFmpeg has a @url{ffmpeg-protocols.html#concat, |
| 349 | @code{concat}} protocol designed specifically for that, with examples in the |
| 350 | documentation. |
| 351 | |
| 352 | A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow one to concatenate |
| 353 | video by merely concatenating the files containing them. |
| 354 | |
| 355 | Hence you may concatenate your multimedia files by first transcoding them to |
| 356 | these privileged formats, then using the humble @code{cat} command (or the |
| 357 | equally humble @code{copy} under Windows), and finally transcoding back to your |
| 358 | format of choice. |
| 359 | |
| 360 | @example |
| 361 | ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg |
| 362 | ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg |
| 363 | cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg |
| 364 | ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi |
| 365 | @end example |
| 366 | |
| 367 | Additionally, you can use the @code{concat} protocol instead of @code{cat} or |
| 368 | @code{copy} which will avoid creation of a potentially huge intermediate file. |
| 369 | |
| 370 | @example |
| 371 | ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg |
| 372 | ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg |
| 373 | ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg |
| 374 | ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi |
| 375 | @end example |
| 376 | |
| 377 | Note that you may need to escape the character "|" which is special for many |
| 378 | shells. |
| 379 | |
| 380 | Another option is usage of named pipes, should your platform support it: |
| 381 | |
| 382 | @example |
| 383 | mkfifo intermediate1.mpg |
| 384 | mkfifo intermediate2.mpg |
| 385 | ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null & |
| 386 | ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null & |
| 387 | cat intermediate1.mpg intermediate2.mpg |\ |
| 388 | ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi |
| 389 | @end example |
| 390 | |
| 391 | @subsection Concatenating using raw audio and video |
| 392 | |
| 393 | Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also |
| 394 | allow concatenation, and the transcoding step is almost lossless. |
| 395 | When using multiple yuv4mpegpipe(s), the first line needs to be discarded |
| 396 | from all but the first stream. This can be accomplished by piping through |
| 397 | @code{tail} as seen below. Note that when piping through @code{tail} you |
| 398 | must use command grouping, @code{@{ ;@}}, to background properly. |
| 399 | |
| 400 | For example, let's say we want to concatenate two FLV files into an |
| 401 | output.flv file: |
| 402 | |
| 403 | @example |
| 404 | mkfifo temp1.a |
| 405 | mkfifo temp1.v |
| 406 | mkfifo temp2.a |
| 407 | mkfifo temp2.v |
| 408 | mkfifo all.a |
| 409 | mkfifo all.v |
| 410 | ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & |
| 411 | ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & |
| 412 | ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & |
| 413 | @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} & |
| 414 | cat temp1.a temp2.a > all.a & |
| 415 | cat temp1.v temp2.v > all.v & |
| 416 | ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \ |
| 417 | -f yuv4mpegpipe -i all.v \ |
| 418 | -y output.flv |
| 419 | rm temp[12].[av] all.[av] |
| 420 | @end example |
| 421 | |
| 422 | @section Using @option{-f lavfi}, audio becomes mono for no apparent reason. |
| 423 | |
| 424 | Use @option{-dumpgraph -} to find out exactly where the channel layout is |
| 425 | lost. |
| 426 | |
| 427 | Most likely, it is through @code{auto-inserted aresample}. Try to understand |
| 428 | why the converting filter was needed at that place. |
| 429 | |
| 430 | Just before the output is a likely place, as @option{-f lavfi} currently |
| 431 | only support packed S16. |
| 432 | |
| 433 | Then insert the correct @code{aformat} explicitly in the filtergraph, |
| 434 | specifying the exact format. |
| 435 | |
| 436 | @example |
| 437 | aformat=sample_fmts=s16:channel_layouts=stereo |
| 438 | @end example |
| 439 | |
| 440 | @section Why does FFmpeg not see the subtitles in my VOB file? |
| 441 | |
| 442 | VOB and a few other formats do not have a global header that describes |
| 443 | everything present in the file. Instead, applications are supposed to scan |
| 444 | the file to see what it contains. Since VOB files are frequently large, only |
| 445 | the beginning is scanned. If the subtitles happen only later in the file, |
| 446 | they will not be initially detected. |
| 447 | |
| 448 | Some applications, including the @code{ffmpeg} command-line tool, can only |
| 449 | work with streams that were detected during the initial scan; streams that |
| 450 | are detected later are ignored. |
| 451 | |
| 452 | The size of the initial scan is controlled by two options: @code{probesize} |
| 453 | (default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For |
| 454 | the subtitle stream to be detected, both values must be large enough. |
| 455 | |
| 456 | @section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead? |
| 457 | |
| 458 | The @option{-sameq} option meant "same quantizer", and made sense only in a |
| 459 | very limited set of cases. Unfortunately, a lot of people mistook it for |
| 460 | "same quality" and used it in places where it did not make sense: it had |
| 461 | roughly the expected visible effect, but achieved it in a very inefficient |
| 462 | way. |
| 463 | |
| 464 | Each encoder has its own set of options to set the quality-vs-size balance, |
| 465 | use the options for the encoder you are using to set the quality level to a |
| 466 | point acceptable for your tastes. The most common options to do that are |
| 467 | @option{-qscale} and @option{-qmax}, but you should peruse the documentation |
| 468 | of the encoder you chose. |
| 469 | |
| 470 | @section I have a stretched video, why does scaling does not fix it? |
| 471 | |
| 472 | A lot of video codecs and formats can store the @emph{aspect ratio} of the |
| 473 | video: this is the ratio between the width and the height of either the full |
| 474 | image (DAR, display aspect ratio) or individual pixels (SAR, sample aspect |
| 475 | ratio). For example, EGA screens at resolution 640×350 had 4:3 DAR and 35:48 |
| 476 | SAR. |
| 477 | |
| 478 | Most still image processing work with square pixels, i.e. 1:1 SAR, but a lot |
| 479 | of video standards, especially from the analogic-numeric transition era, use |
| 480 | non-square pixels. |
| 481 | |
| 482 | Most processing filters in FFmpeg handle the aspect ratio to avoid |
| 483 | stretching the image: cropping adjusts the DAR to keep the SAR constant, |
| 484 | scaling adjusts the SAR to keep the DAR constant. |
| 485 | |
| 486 | If you want to stretch, or “unstretch”, the image, you need to override the |
| 487 | information with the |
| 488 | @url{ffmpeg-filters.html#setdar_002c-setsar, @code{setdar or setsar filters}}. |
| 489 | |
| 490 | Do not forget to examine carefully the original video to check whether the |
| 491 | stretching comes from the image or from the aspect ratio information. |
| 492 | |
| 493 | For example, to fix a badly encoded EGA capture, use the following commands, |
| 494 | either the first one to upscale to square pixels or the second one to set |
| 495 | the correct aspect ratio or the third one to avoid transcoding (may not work |
| 496 | depending on the format / codec / player / phase of the moon): |
| 497 | |
| 498 | @example |
| 499 | ffmpeg -i ega_screen.nut -vf scale=640:480,setsar=1 ega_screen_scaled.nut |
| 500 | ffmpeg -i ega_screen.nut -vf setdar=4/3 ega_screen_anamorphic.nut |
| 501 | ffmpeg -i ega_screen.nut -aspect 4/3 -c copy ega_screen_overridden.nut |
| 502 | @end example |
| 503 | |
| 504 | @chapter Development |
| 505 | |
| 506 | @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat? |
| 507 | |
| 508 | Yes. Check the @file{doc/examples} directory in the source |
| 509 | repository, also available online at: |
| 510 | @url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}. |
| 511 | |
| 512 | Examples are also installed by default, usually in |
| 513 | @code{$PREFIX/share/ffmpeg/examples}. |
| 514 | |
| 515 | Also you may read the Developers Guide of the FFmpeg documentation. Alternatively, |
| 516 | examine the source code for one of the many open source projects that |
| 517 | already incorporate FFmpeg at (@url{projects.html}). |
| 518 | |
| 519 | @section Can you support my C compiler XXX? |
| 520 | |
| 521 | It depends. If your compiler is C99-compliant, then patches to support |
| 522 | it are likely to be welcome if they do not pollute the source code |
| 523 | with @code{#ifdef}s related to the compiler. |
| 524 | |
| 525 | @section Is Microsoft Visual C++ supported? |
| 526 | |
| 527 | Yes. Please see the @uref{platform.html, Microsoft Visual C++} |
| 528 | section in the FFmpeg documentation. |
| 529 | |
| 530 | @section Can you add automake, libtool or autoconf support? |
| 531 | |
| 532 | No. These tools are too bloated and they complicate the build. |
| 533 | |
| 534 | @section Why not rewrite FFmpeg in object-oriented C++? |
| 535 | |
| 536 | FFmpeg is already organized in a highly modular manner and does not need to |
| 537 | be rewritten in a formal object language. Further, many of the developers |
| 538 | favor straight C; it works for them. For more arguments on this matter, |
| 539 | read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}. |
| 540 | |
| 541 | @section Why are the ffmpeg programs devoid of debugging symbols? |
| 542 | |
| 543 | The build process creates @command{ffmpeg_g}, @command{ffplay_g}, etc. which |
| 544 | contain full debug information. Those binaries are stripped to create |
| 545 | @command{ffmpeg}, @command{ffplay}, etc. If you need the debug information, use |
| 546 | the *_g versions. |
| 547 | |
| 548 | @section I do not like the LGPL, can I contribute code under the GPL instead? |
| 549 | |
| 550 | Yes, as long as the code is optional and can easily and cleanly be placed |
| 551 | under #if CONFIG_GPL without breaking anything. So, for example, a new codec |
| 552 | or filter would be OK under GPL while a bug fix to LGPL code would not. |
| 553 | |
| 554 | @section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves. |
| 555 | |
| 556 | FFmpeg builds static libraries by default. In static libraries, dependencies |
| 557 | are not handled. That has two consequences. First, you must specify the |
| 558 | libraries in dependency order: @code{-lavdevice} must come before |
| 559 | @code{-lavformat}, @code{-lavutil} must come after everything else, etc. |
| 560 | Second, external libraries that are used in FFmpeg have to be specified too. |
| 561 | |
| 562 | An easy way to get the full list of required libraries in dependency order |
| 563 | is to use @code{pkg-config}. |
| 564 | |
| 565 | @example |
| 566 | c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec) |
| 567 | @end example |
| 568 | |
| 569 | See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for |
| 570 | more details. |
| 571 | |
| 572 | @section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available. |
| 573 | |
| 574 | FFmpeg is a pure C project, so to use the libraries within your C++ application |
| 575 | you need to explicitly state that you are using a C library. You can do this by |
| 576 | encompassing your FFmpeg includes using @code{extern "C"}. |
| 577 | |
| 578 | See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3} |
| 579 | |
| 580 | @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope |
| 581 | |
| 582 | FFmpeg is a pure C project using C99 math features, in order to enable C++ |
| 583 | to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS |
| 584 | |
| 585 | @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat? |
| 586 | |
| 587 | You have to create a custom AVIOContext using @code{avio_alloc_context}, |
| 588 | see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources. |
| 589 | |
| 590 | @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm? |
| 591 | |
| 592 | see @url{https://www.ffmpeg.org/~michael/} |
| 593 | |
| 594 | @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec? |
| 595 | |
| 596 | Even if peculiar since it is network oriented, RTP is a container like any |
| 597 | other. You have to @emph{demux} RTP before feeding the payload to libavcodec. |
| 598 | In this specific case please look at RFC 4629 to see how it should be done. |
| 599 | |
| 600 | @section AVStream.r_frame_rate is wrong, it is much larger than the frame rate. |
| 601 | |
| 602 | @code{r_frame_rate} is NOT the average frame rate, it is the smallest frame rate |
| 603 | that can accurately represent all timestamps. So no, it is not |
| 604 | wrong if it is larger than the average! |
| 605 | For example, if you have mixed 25 and 30 fps content, then @code{r_frame_rate} |
| 606 | will be 150 (it is the least common multiple). |
| 607 | If you are looking for the average frame rate, see @code{AVStream.avg_frame_rate}. |
| 608 | |
| 609 | @section Why is @code{make fate} not running all tests? |
| 610 | |
| 611 | Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable |
| 612 | or @code{FATE_SAMPLES} environment variable or the @code{--samples} |
| 613 | @command{configure} option is set to the right path. |
| 614 | |
| 615 | @section Why is @code{make fate} not finding the samples? |
| 616 | |
| 617 | Do you happen to have a @code{~} character in the samples path to indicate a |
| 618 | home directory? The value is used in ways where the shell cannot expand it, |
| 619 | causing FATE to not find files. Just replace @code{~} by the full path. |
| 620 | |
| 621 | @bye |
| 622 |