
  FFmpeg FAQ


    Table of Contents

  *
    1 General Questions

    <#General-Questions>
      o
        1.1 Why doesn’t FFmpeg support feature [xyz]?

        <#Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f>
      o
        1.2 FFmpeg does not support codec XXX. Can you include a Windows
        DLL loader to support it?

        <#FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f>
      o
        1.3 I cannot read this file although this format seems to be
        supported by ffmpeg.

        <#I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e>
      o
        1.4 Which codecs are supported by Windows?

        <#Which-codecs-are-supported-by-Windows_003f>
  *
    2 Compilation

    <#Compilation>
      o
        2.1 |error: can't find a register in class 'GENERAL_REGS' while
        reloading 'asm'|

        <#error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027>
      o
        2.2 I have installed this library with my distro’s package
        manager. Why does |configure| not see it?

        <#I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f>
      o
        2.3 How do I make |pkg-config| find my libraries?

        <#How-do-I-make-pkg_002dconfig-find-my-libraries_003f>
      o
        2.4 How do I use |pkg-config| when cross-compiling?

        <#How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f>
  *
    3 Usage

    <#Usage>
      o
        3.1 ffmpeg does not work; what is wrong?

        <#ffmpeg-does-not-work_003b-what-is-wrong_003f>
      o
        3.2 How do I encode single pictures into movies?

        <#How-do-I-encode-single-pictures-into-movies_003f>
      o
        3.3 How do I encode movie to single pictures?

        <#How-do-I-encode-movie-to-single-pictures_003f>
      o
        3.4 Why do I see a slight quality degradation with multithreaded
        MPEG* encoding?

        <#Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f>
      o
        3.5 How can I read from the standard input or write to the
        standard output?

        <#How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f>
      o
        3.6 -f jpeg doesn’t work.

        <#g_t_002df-jpeg-doesn_0027t-work_002e>
      o
        3.7 Why can I not change the frame rate?

        <#Why-can-I-not-change-the-frame-rate_003f>
      o
        3.8 How do I encode Xvid or DivX video with ffmpeg?

        <#How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f>
      o
        3.9 Which are good parameters for encoding high quality MPEG-4?

        <#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f>
      o
        3.10 Which are good parameters for encoding high quality
        MPEG-1/MPEG-2?

        <#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f>
      o
        3.11 Interlaced video looks very bad when encoded with ffmpeg,
        what is wrong?

        <#Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f>
      o
        3.12 How can I read DirectShow files?

        <#How-can-I-read-DirectShow-files_003f>
      o
        3.13 How can I join video files?

        <#How-can-I-join-video-files_003f>
      o
        3.14 How can I concatenate video files?

        <#How-can-I-concatenate-video-files_003f>
          +
            3.14.1 Concatenating using the concat /filter/

            <#Concatenating-using-the-concat-filter>
          +
            3.14.2 Concatenating using the concat /demuxer/

            <#Concatenating-using-the-concat-demuxer>
          +
            3.14.3 Concatenating using the concat /protocol/ (file level)

            <#Concatenating-using-the-concat-protocol-_0028file-level_0029>
          +
            3.14.4 Concatenating using raw audio and video

            <#Concatenating-using-raw-audio-and-video>
      o
        3.15 Using -f lavfi, audio becomes mono for no apparent reason.

        <#Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e>
      o
        3.16 Why does FFmpeg not see the subtitles in my VOB file?

        <#Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f>
      o
        3.17 Why was the |ffmpeg| -sameq option removed? What to use
        instead?

        <#Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f>
      o
        3.18 I have a stretched video, why does scaling does not fix it?

        <#I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f>
      o
        3.19 How do I run ffmpeg as a background task?

        <#How-do-I-run-ffmpeg-as-a-background-task_003f>
      o
        3.20 How do I prevent ffmpeg from suspending with a message like
        /suspended (tty output)/?

        <#How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f>
  *
    4 Development

    <#Development>
      o
        4.1 Are there examples illustrating how to use the FFmpeg
        libraries, particularly libavcodec and libavformat?

        <#Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f>
      o
        4.2 Can you support my C compiler XXX?

        <#Can-you-support-my-C-compiler-XXX_003f>
      o
        4.3 Is Microsoft Visual C++ supported?

        <#Is-Microsoft-Visual-C_002b_002b-supported_003f>
      o
        4.4 Can you add automake, libtool or autoconf support?

        <#Can-you-add-automake_002c-libtool-or-autoconf-support_003f>
      o
        4.5 Why not rewrite FFmpeg in object-oriented C++?

        <#Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f>
      o
        4.6 Why are the ffmpeg programs devoid of debugging symbols?

        <#Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f>
      o
        4.7 I do not like the LGPL, can I contribute code under the GPL
        instead?

        <#I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f>
      o
        4.8 I’m using FFmpeg from within my C application but the linker
        complains about missing symbols from the libraries themselves.

        <#I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e>
      o
        4.9 I’m using FFmpeg from within my C++ application but the
        linker complains about missing symbols which seem to be available.

        <#I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e>
      o
        4.10 I’m using libavutil from within my C++ application but the
        compiler complains about ’UINT64_C’ was not declared in this scope

        <#I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope>
      o
        4.11 I have a file in memory / a API different from *open/*read/
        libc how do I use it with libavformat?

        <#I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f>
      o
        4.12 Where is the documentation about ffv1, msmpeg4, asv1, 4xm?

        <#Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f>
      o
        4.13 How do I feed H.263-RTP (and other codecs in RTP) to
        libavcodec?

        <#How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f>
      o
        4.14 AVStream.r_frame_rate is wrong, it is much larger than the
        frame rate.

        <#AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e>
      o
        4.15 Why is |make fate| not running all tests?

        <#Why-is-make-fate-not-running-all-tests_003f>
      o
        4.16 Why is |make fate| not finding the samples?

        <#Why-is-make-fate-not-finding-the-samples_003f>

  *
    General Questions

    <#General-Questions>
  *
    Compilation

    <#Compilation>
  *
    Usage

    <#Usage>
  *
    Development

    <#Development>


    1 General Questions

  *
    Why doesn’t FFmpeg support feature [xyz]?

    <#Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f>
  *
    FFmpeg does not support codec XXX. Can you include a Windows DLL
    loader to support it?

    <#FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f>
  *
    I cannot read this file although this format seems to be supported
    by ffmpeg.

    <#I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e>
  *
    Which codecs are supported by Windows?

    <#Which-codecs-are-supported-by-Windows_003f>


      1.1 Why doesn’t FFmpeg support feature [xyz]?

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.


      1.2 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
FFmpeg strives to support all codecs natively. A DLL loader is not
conducive to that goal.


      1.3 I cannot read this file although this format seems to be
      supported by ffmpeg.

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.


      1.4 Which codecs are supported by Windows?

Windows does not support standard formats like MPEG very well, unless
you install some additional codecs.

The following list of video codecs should work on most Windows systems:

msmpeg4v2

    .avi/.asf

msmpeg4

    .asf only

wmv1

    .asf only

wmv2

    .asf only

mpeg4

    Only if you have some MPEG-4 codec like ffdshow or Xvid installed.

mpeg1video

    .mpg only

Note, ASF files often have .wmv or .wma extensions in Windows. It should
also be mentioned that Microsoft claims a patent on the ASF format, and
may sue or threaten users who create ASF files with non-Microsoft
software. It is strongly advised to avoid ASF where possible.

The following list of audio codecs should work on most Windows systems:

adpcm_ima_wav
adpcm_ms
pcm_s16le

    always

libmp3lame

    If some MP3 codec like LAME is installed.


    2 Compilation

  *
    |error: can't find a register in class 'GENERAL_REGS' while
    reloading 'asm'|

    <#error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027>
  *
    I have installed this library with my distro’s package manager. Why
    does |configure| not see it?

    <#I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f>
  *
    How do I make |pkg-config| find my libraries?

    <#How-do-I-make-pkg_002dconfig-find-my-libraries_003f>
  *
    How do I use |pkg-config| when cross-compiling?

    <#How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f>


      2.1 |error: can't find a register in class 'GENERAL_REGS' while
      reloading 'asm'|

This is a bug in gcc. Do not report it to us. Instead, please report it
to the gcc developers. Note that we will not add workarounds for gcc bugs.

Also note that (some of) the gcc developers believe this is not a bug or
not a bug they should fix:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203

. Then again, some of them do not know the difference between an
undecidable problem and an NP-hard problem...


      2.2 I have installed this library with my distro’s package
      manager. Why does |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 libfoo-dev or libfoo-devel. You can remove it after the
build is finished, but be sure to keep the main package.


      2.3 How do I make |pkg-config| find my libraries?

Somewhere along with your libraries, there is a .pc file (or several) in
a pkgconfig directory. You need to set environment variables to point
|pkg-config| to these files.

If you need to /add/ directories to |pkg-config|’s search list (typical
use case: library installed separately), add it to |$PKG_CONFIG_PATH|:

export PKG_CONFIG_PATH=/opt/x264/lib/pkgconfig:/opt/opus/lib/pkgconfig

If you need to /replace/ |pkg-config|’s search list (typical use case:
cross-compiling), set it in |$PKG_CONFIG_LIBDIR|:

export PKG_CONFIG_LIBDIR=/home/me/cross/usr/lib/pkgconfig:/home/me/cross/usr/local/lib/pkgconfig

If you need to know the library’s internal dependencies (typical use:
static linking), add the |--static| option to |pkg-config|:

./configure --pkg-config-flags=--static


      2.4 How do I use |pkg-config| when cross-compiling?

The best way is to install |pkg-config| in your cross-compilation
environment. It will automatically use the cross-compilation libraries.

You can also use |pkg-config| from the host environment by specifying
explicitly |--pkg-config=pkg-config| to |configure|. In that case, you
must point |pkg-config| to the correct directories using the
|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 |pkg-config| with
|PKG_CONFIG_LIBDIR| set. That script can look like that:

#!/bin/sh
PKG_CONFIG_LIBDIR=/path/to/cross/lib/pkgconfig
export PKG_CONFIG_LIBDIR
exec /usr/bin/pkg-config "$@"


    3 Usage

  *
    ffmpeg does not work; what is wrong?

    <#ffmpeg-does-not-work_003b-what-is-wrong_003f>
  *
    How do I encode single pictures into movies?

    <#How-do-I-encode-single-pictures-into-movies_003f>
  *
    How do I encode movie to single pictures?

    <#How-do-I-encode-movie-to-single-pictures_003f>
  *
    Why do I see a slight quality degradation with multithreaded MPEG*
    encoding?

    <#Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f>
  *
    How can I read from the standard input or write to the standard output?

    <#How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f>
  *
    -f jpeg doesn’t work.

    <#g_t_002df-jpeg-doesn_0027t-work_002e>
  *
    Why can I not change the frame rate?

    <#Why-can-I-not-change-the-frame-rate_003f>
  *
    How do I encode Xvid or DivX video with ffmpeg?

    <#How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f>
  *
    Which are good parameters for encoding high quality MPEG-4?

    <#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f>
  *
    Which are good parameters for encoding high quality MPEG-1/MPEG-2?

    <#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f>
  *
    Interlaced video looks very bad when encoded with ffmpeg, what is wrong?

    <#Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f>
  *
    How can I read DirectShow files?

    <#How-can-I-read-DirectShow-files_003f>
  *
    How can I join video files?

    <#How-can-I-join-video-files_003f>
  *
    How can I concatenate video files?

    <#How-can-I-concatenate-video-files_003f>
  *
    Using -f lavfi, audio becomes mono for no apparent reason.

    <#Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e>
  *
    Why does FFmpeg not see the subtitles in my VOB file?

    <#Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f>
  *
    Why was the |ffmpeg| -sameq option removed? What to use instead?

    <#Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f>
  *
    I have a stretched video, why does scaling does not fix it?

    <#I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f>
  *
    How do I run ffmpeg as a background task?

    <#How-do-I-run-ffmpeg-as-a-background-task_003f>
  *
    How do I prevent ffmpeg from suspending with a message like
    /suspended (tty output)/?

    <#How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f>


      3.1 ffmpeg does not work; what is wrong?

Try a |make distclean| in the ffmpeg source directory before the build.
If this does not help see (
https://ffmpeg.org/bugreports.html

).


      3.2 How do I encode single pictures into movies?

First, rename your pictures to follow a numerical sequence. For example,
img1.jpg, img2.jpg, img3.jpg,... Then you may run:

ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg

Notice that ‘%d’ is replaced by the image number.

img%03d.jpg means the sequence img001.jpg, img002.jpg, etc.

Use the -start_number option to declare a starting number for the
sequence. This is useful if your sequence does not start with img001.jpg
but is still in a numerical order. The following example will start with
img100.jpg:

ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg

If you have large number of pictures to rename, you can use the
following command to ease the burden. The command, using the bourne
shell syntax, symbolically links all files in the current directory that
match |*jpg| to the /tmp directory in the sequence of img001.jpg,
img002.jpg and so on.

x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done

If you want to sequence them by oldest modified first, substitute |$(ls
-r -t *jpg)| in place of |*jpg|.

Then run:

ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg

The same logic is used for any image format that ffmpeg reads.

You can also use |cat| to pipe images to ffmpeg:

cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg


      3.3 How do I encode movie to single pictures?

Use:

ffmpeg -i movie.mpg movie%d.jpg

The movie.mpg used as input will be converted to movie1.jpg, movie2.jpg,
etc...

Instead of relying on file format self-recognition, you may also use

-c:v ppm
-c:v png
-c:v mjpeg

to force the encoding.

Applying that to the previous example:

ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg

Beware that there is no "jpeg" codec. Use "mjpeg" instead.


      3.4 Why do I see a slight quality degradation with multithreaded
      MPEG* encoding?

For multithreaded MPEG* encoding, the encoded slices must be
independent, otherwise thread n would practically have to wait for n-1
to finish, so it’s quite logical that there is a small reduction of
quality. This is not a bug.


      3.5 How can I read from the standard input or write to the
      standard output?

Use - as file name.


      3.6 -f jpeg doesn’t work.

Try ’-f image2 test%d.jpg’.


      3.7 Why can I not change the frame rate?

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.


      3.8 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
same standard). Thus, use ’-c:v mpeg4’ to encode in these formats. The
default fourcc stored in an MPEG-4-coded file will be ’FMP4’. If you
want a different fourcc, use the ’-vtag’ option. E.g., ’-vtag xvid’ will
force the fourcc ’xvid’ to be stored as the video fourcc rather than the
default.


      3.9 Which are good parameters for encoding high quality MPEG-4?

’-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2’,
things to try: ’-bf 2’, ’-mpv_flags qp_rd’, ’-mpv_flags mv0’,
’-mpv_flags skip_rd’.


      3.10 Which are good parameters for encoding high quality
      MPEG-1/MPEG-2?

’-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2’ but beware the
’-g 100’ might cause problems with some decoders. Things to try: ’-bf
2’, ’-mpv_flags qp_rd’, ’-mpv_flags mv0’, ’-mpv_flags skip_rd’.


      3.11 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.


      3.12 How can I read DirectShow files?

If you have built FFmpeg with |./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 ...

DirectShowSource("C:\path to your file\yourfile.asf")

... and then feed that text file to ffmpeg:

ffmpeg -i input.avs

For ANY other help on AviSynth, please visit the
AviSynth homepage

<http://www.avisynth.org/>.


      3.13 How can I join video files?

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:

  * To put them one after the other: this is called to /concatenate/
    them (in short: concat) and is addressed
    in this very faq

    <#How-can-I-concatenate-video-files>.
  * 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 /multiplex/ them together (in short: mux), and is
    done by simply invoking ffmpeg with several -i options.
  * For audio, to put all channels together in a single stream (example:
    two mono streams into one stereo stream): this is sometimes called
    to /merge/ them, and can be done using the
    |amerge|

    <file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-filters.html#amerge>
    filter.
  * For audio, to play one on top of the other: this is called to /mix/
    them, and can be done by first merging them into a single stream and
    then using the
    |pan|

    <file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-filters.html#pan>
    filter to mix the channels at will.
  * 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
    |overlay|

    <file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-filters.html#overlay>
    video filter. 


      3.14 How can I concatenate video files?

There are several solutions, depending on the exact circumstances.

  *
    Concatenating using the concat /filter/

    <#Concatenating-using-the-concat-filter>
  *
    Concatenating using the concat /demuxer/

    <#Concatenating-using-the-concat-demuxer>
  *
    Concatenating using the concat /protocol/ (file level)

    <#Concatenating-using-the-concat-protocol-_0028file-level_0029>
  *
    Concatenating using raw audio and video

    <#Concatenating-using-raw-audio-and-video>


        3.14.1 Concatenating using the concat /filter/

FFmpeg has a
|concat|

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-filters.html#concat>
filter designed specifically for that, with examples in the
documentation. This operation is recommended if you need to re-encode.


        3.14.2 Concatenating using the concat /demuxer/

FFmpeg has a
|concat|

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-formats.html#concat>
demuxer which you can use when you want to avoid a re-encode and your
format doesn’t support file level concatenation.


        3.14.3 Concatenating using the concat /protocol/ (file level)

FFmpeg has a
|concat|

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-protocols.html#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 |cat| command
(or the equally humble |copy| under Windows), and finally transcoding
back to your format of choice.

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
ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi

Additionally, you can use the |concat| protocol instead of |cat| or
|copy| which will avoid creation of a potentially huge intermediate file.

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

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:

mkfifo intermediate1.mpg
mkfifo intermediate2.mpg
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 |\
ffmpeg -f mpeg -i - -c:v mpeg4 -c:a libmp3lame output.avi


        3.14.4 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 from all but the first stream. This can be accomplished by
piping through |tail| as seen below. Note that when piping through
|tail| you must use command grouping, |{ ;}|, to background properly.

For example, let’s say we want to concatenate two FLV files into an
output.flv file:

mkfifo temp1.a
mkfifo temp1.v
mkfifo temp2.a
mkfifo temp2.v
mkfifo all.a
mkfifo all.v
ffmpeg -i input1.flv -vn -f u16le -c:a pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
ffmpeg -i input2.flv -vn -f u16le -c:a 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 &
ffmpeg -f u16le -c:a pcm_s16le -ac 2 -ar 44100 -i all.a \
       -f yuv4mpegpipe -i all.v \
       -y output.flv
rm temp[12].[av] all.[av]


      3.15 Using -f lavfi, audio becomes mono for no apparent reason.

Use -dumpgraph - to find out exactly where the channel layout is lost.

Most likely, it is through |auto-inserted aresample|. Try to understand
why the converting filter was needed at that place.

Just before the output is a likely place, as -f lavfi currently only
support packed S16.

Then insert the correct |aformat| explicitly in the filtergraph,
specifying the exact format.

aformat=sample_fmts=s16:channel_layouts=stereo


      3.16 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 |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: |probesize|
(default ~5 Mo) and |analyzeduration| (default 5,000,000 µs = 5 s). For
the subtitle stream to be detected, both values must be large enough.


      3.17 Why was the |ffmpeg| -sameq option removed? What to use instead?

The -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 -qscale and -qmax, but you should peruse the
documentation of the encoder you chose.


      3.18 I have a stretched video, why does scaling does not fix it?

A lot of video codecs and formats can store the /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.

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.

If you want to stretch, or “unstretch”, the image, you need to override
the information with the
|setdar or setsar filters|

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg-filters.html#setdar_002c-setsar>.


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):

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


      3.19 How do I run ffmpeg as a background task?

ffmpeg normally checks the console input, for entries like "q" to stop
and "?" to give help, while performing operations. ffmpeg does not have
a way of detecting when it is running as a background task. When it
checks the console input, that can cause the process running ffmpeg in
the background to suspend.

To prevent those input checks, allowing ffmpeg to run as a background
task, use the
|-nostdin| option

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg.html#stdin-option>
in the ffmpeg invocation. This is effective whether you run ffmpeg in a
shell or invoke ffmpeg in its own process via an operating system API.

As an alternative, when you are running ffmpeg in a shell, you can
redirect standard input to |/dev/null| (on Linux and macOS) or |NUL| (on
Windows). You can do this redirect either on the ffmpeg invocation, or
from a shell script which calls ffmpeg.

For example:

ffmpeg -nostdin -i INPUT OUTPUT

or (on Linux, macOS, and other UNIX-like shells):

ffmpeg -i INPUT OUTPUT </dev/null

or (on Windows):

ffmpeg -i INPUT OUTPUT <NUL


      3.20 How do I prevent ffmpeg from suspending with a message like
      /suspended (tty output)/?

If you run ffmpeg in the background, you may find that its process
suspends. There may be a message like /suspended (tty output)/. The
question is how to prevent the process from being suspended.

For example:

% ffmpeg -i INPUT OUTPUT &> ~/tmp/log.txt &
[1] 93352
%
[1]  + suspended (tty output)  ffmpeg -i INPUT OUTPUT &>

The message "tty output" notwithstanding, the problem here is that
ffmpeg normally checks the console input when it runs. The operating
system detects this, and suspends the process until you can bring it to
the foreground and attend to it.

The solution is to use the right techniques to tell ffmpeg not to
consult console input. You can use the
|-nostdin| option

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/ffmpeg.html#stdin-option>,
or redirect standard input with |< /dev/null|. See FAQ
/How do I run ffmpeg as a background task?/

<#background-task> for details.


    4 Development

  *
    Are there examples illustrating how to use the FFmpeg libraries,
    particularly libavcodec and libavformat?

    <#Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f>
  *
    Can you support my C compiler XXX?

    <#Can-you-support-my-C-compiler-XXX_003f>
  *
    Is Microsoft Visual C++ supported?

    <#Is-Microsoft-Visual-C_002b_002b-supported_003f>
  *
    Can you add automake, libtool or autoconf support?

    <#Can-you-add-automake_002c-libtool-or-autoconf-support_003f>
  *
    Why not rewrite FFmpeg in object-oriented C++?

    <#Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f>
  *
    Why are the ffmpeg programs devoid of debugging symbols?

    <#Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f>
  *
    I do not like the LGPL, can I contribute code under the GPL instead?

    <#I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f>
  *
    I’m using FFmpeg from within my C application but the linker
    complains about missing symbols from the libraries themselves.

    <#I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e>
  *
    I’m using FFmpeg from within my C++ application but the linker
    complains about missing symbols which seem to be available.

    <#I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e>
  *
    I’m using libavutil from within my C++ application but the compiler
    complains about ’UINT64_C’ was not declared in this scope

    <#I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope>
  *
    I have a file in memory / a API different from *open/*read/ libc how
    do I use it with libavformat?

    <#I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f>
  *
    Where is the documentation about ffv1, msmpeg4, asv1, 4xm?

    <#Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f>
  *
    How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?

    <#How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f>
  *
    AVStream.r_frame_rate is wrong, it is much larger than the frame rate.

    <#AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e>
  *
    Why is |make fate| not running all tests?

    <#Why-is-make-fate-not-running-all-tests_003f>
  *
    Why is |make fate| not finding the samples?

    <#Why-is-make-fate-not-finding-the-samples_003f>


      4.1 Are there examples illustrating how to use the FFmpeg
      libraries, particularly libavcodec and libavformat?

Yes. Check the doc/examples directory in the source repository, also
available online at:
https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples

.

Examples are also installed by default, usually in
|$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 FFmpeg at (
projects.html

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/projects.html>).


      4.2 Can you support my C compiler XXX?

It depends. If your compiler is C99-compliant, then patches to support
it are likely to be welcome if they do not pollute the source code with
|#ifdef|s related to the compiler.


      4.3 Is Microsoft Visual C++ supported?

Yes. Please see the
Microsoft Visual C++

<file:///C:/Utils/ffmpeg-6.1.1-essentials_build/doc/platform.html>
section in the FFmpeg documentation.


      4.4 Can you add automake, libtool or autoconf support?

No. These tools are too bloated and they complicate the build.


      4.5 Why not rewrite FFmpeg in object-oriented C++?

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
"Programming Religion"

<https://web.archive.org/web/20111004021423/http://kernel.org/pub/linux/docs/lkml/#s15>.



      4.6 Why are the ffmpeg programs devoid of debugging symbols?

The build process creates |ffmpeg_g|, |ffplay_g|, etc. which contain
full debug information. Those binaries are stripped to create |ffmpeg|,
|ffplay|, etc. If you need the debug information, use the *_g versions.


      4.7 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 or filter would be OK under GPL while a bug fix to LGPL code
would not.


      4.8 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: |-lavdevice| must come before
|-lavformat|, |-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 |pkg-config|.

c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)

See doc/example/Makefile and doc/example/pc-uninstalled for more details.


      4.9 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 FFmpeg includes using |extern "C"|.

See
http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3


      4.10 I’m using libavutil from within my C++ application but the
      compiler complains about ’UINT64_C’ was not declared in this scope

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


      4.11 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 |avio_alloc_context|, see
libavformat/aviobuf.c in FFmpeg and libmpdemux/demux_lavf.c in MPlayer
or MPlayer2 sources.


      4.12 Where is the documentation about ffv1, msmpeg4, asv1, 4xm?

see
https://www.ffmpeg.org/~michael/


      4.13 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 /demux/ RTP before feeding the payload to
libavcodec. In this specific case please look at RFC 4629 to see how it
should be done.


      4.14 AVStream.r_frame_rate is wrong, it is much larger than the
      frame rate.

|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 |r_frame_rate| will be 150 (it is the least
common multiple). If you are looking for the average frame rate, see
|AVStream.avg_frame_rate|.


      4.15 Why is |make fate| not running all tests?

Make sure you have the fate-suite samples and the |SAMPLES| Make
variable or |FATE_SAMPLES| environment variable or the |--samples|
|configure| option is set to the right path.


      4.16 Why is |make fate| not finding the samples?

Do you happen to have a |~| character in the samples path to indicate a
home directory? The value is used in ways where the shell cannot expand
it, causing FATE to not find files. Just replace |~| by the full path.

This document was generated using
/makeinfo/

<https://www.gnu.org/software/texinfo/>.

