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In fact I have succeeded to convert FLV to MP3:

D:\tmp\ffmpeg-20121005-git-d9dfe9a-win64-static\ffmpeg-20121005-git-d9dfe9a-win
4-static\bin>ffmpeg.exe -i a.flv -acodec mp3 a.mp3
ffmpeg version N-45080-gd9dfe9a Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct  5 2012 16:49:01 with gcc 4.7.1 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-pthreads --enable-run
ime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass
-enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-
ibfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopen
peg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libthe
ra --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-l
bvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --en
ble-zlib
  libavutil      51. 73.102 / 51. 73.102
  libavcodec     54. 63.100 / 54. 63.100
  libavformat    54. 29.105 / 54. 29.105
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
Input #0, flv, from 'a.flv':
  Metadata:
    metadatacreator : iku
    hasKeyframes    : true
    hasVideo        : true
    hasAudio        : true
    hasMetadata     : true
    canSeekToEnd    : false
    datasize        : 16906383
    videosize       : 14558526
    audiosize       : 2270465
    lasttimestamp   : 530
    lastkeyframetimestamp: 529
    lastkeyframelocation: 16893721
  Duration: 00:08:49.73, start: 0.000000, bitrate: 255 kb/s
    Stream #0:0: Video: h264 (Main), yuv420p, 448x336 [SAR 1:1 DAR 4:3], 218 kb
s, 15 tbr, 1k tbn, 30 tbc
    Stream #0:1: Audio: aac, 44100 Hz, stereo, s16, 32 kb/s
File 'a.mp3' already exists. Overwrite ? [y/N] y
Output #0, mp3, to 'a.mp3':
  Metadata:
    metadatacreator : iku
    hasKeyframes    : true
    hasVideo        : true
    hasAudio        : true
    hasMetadata     : true
    canSeekToEnd    : false
    datasize        : 16906383
    videosize       : 14558526
    audiosize       : 2270465
    lasttimestamp   : 530
    lastkeyframetimestamp: 529
    lastkeyframelocation: 16893721
    TSSE            : Lavf54.29.105
    Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16
Stream mapping:
  Stream #0:1 -> #0:0 (aac -> libmp3lame)
Press [q] to stop, [?] for help
size=    8279kB time=00:08:49.78 bitrate= 128.0kbits/s
video:0kB audio:8278kB subtitle:0 global headers:0kB muxing overhead 0.006842%

But I failed to convert FLV to MP4. Why is the encoder 'mp4' unknown? What's more, how can I find the codecs which are already supported by my FFmpeg?

D:\tmp\ffmpeg-20121005-git-d9dfe9a-win64-static\ffmpeg-20121005-git-d9dfe9a-win6
4-static\bin>ffmpeg.exe -i a.flv -acodec mp4 aa.mp4
ffmpeg version N-45080-gd9dfe9a Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct  5 2012 16:49:01 with gcc 4.7.1 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-pthreads --enable-runt
ime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass -
-enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-l
ibfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenj
peg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheo
ra --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-li
bvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --ena
ble-zlib
  libavutil      51. 73.102 / 51. 73.102
  libavcodec     54. 63.100 / 54. 63.100
  libavformat    54. 29.105 / 54. 29.105
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
Input #0, flv, from 'a.flv':
  Metadata:
    metadatacreator : iku
    hasKeyframes    : true
    hasVideo        : true
    hasAudio        : true
    hasMetadata     : true
    canSeekToEnd    : false
    datasize        : 16906383
    videosize       : 14558526
    audiosize       : 2270465
    lasttimestamp   : 530
    lastkeyframetimestamp: 529
    lastkeyframelocation: 16893721
  Duration: 00:08:49.73, start: 0.000000, bitrate: 255 kb/s
    Stream #0:0: Video: h264 (Main), yuv420p, 448x336 [SAR 1:1 DAR 4:3], 218 kb/
s, 15 tbr, 1k tbn, 30 tbc
    Stream #0:1: Audio: aac, 44100 Hz, stereo, s16, 32 kb/s
Unknown encoder 'mp4'

Edit 1: 

[bigmeow@home bin]$ ./ffmpeg -formats | wc -l
ffmpeg version N-45533-gb08273c Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct 15 2012 17:59:59 with gcc 4.1.2 (GCC) 20080704 (Red Hat 4.1.2-52)
  configuration: --disable-yasm --prefix=/var/lib/gforge/chroot/home/users/mirror/ins/ins-ffmpeg
  libavutil      51. 76.100 / 51. 76.100
  libavcodec     54. 66.100 / 54. 66.100
  libavformat    54. 32.101 / 54. 32.101
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
221

Edit 2: cannot use libfaac codec, why?

4-static\bin>ffmpeg -i a.flv -c:a libfaac -vn aa2x.m4a
ffmpeg version N-45080-gd9dfe9a Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct  5 2012 16:49:01 with gcc 4.7.1 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-pthreads --enable-runt
ime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass -
-enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-l
ibfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenj
peg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheo
ra --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-li
bvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --ena
ble-zlib
  libavutil      51. 73.102 / 51. 73.102
  libavcodec     54. 63.100 / 54. 63.100
  libavformat    54. 29.105 / 54. 29.105
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
Input #0, flv, from 'a.flv':
  Metadata:
    metadatacreator : iku
    hasKeyframes    : true
    hasVideo        : true
    hasAudio        : true
    hasMetadata     : true
    canSeekToEnd    : false
    datasize        : 16906383
    videosize       : 14558526
    audiosize       : 2270465
    lasttimestamp   : 530
    lastkeyframetimestamp: 529
    lastkeyframelocation: 16893721
  Duration: 00:08:49.73, start: 0.000000, bitrate: 255 kb/s
    Stream #0:0: Video: h264 (Main), yuv420p, 448x336 [SAR 1:1 DAR 4:3], 218 kb/
s, 15 tbr, 1k tbn, 30 tbc
    Stream #0:1: Audio: aac, 44100 Hz, stereo, s16, 32 kb/s
Unknown encoder 'libfaac'

D:\tmp\ffmpeg-20121005-git-d9dfe9a-win64-static\ffmpeg-20121005-git-d9dfe9a-win6
hugemeow
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1 Answers1

5

Why you can't "convert to MP4 video":

Here's why it doesn't work:

  • What you know as "MP3" is MPEG-2 Layer III, an audio codec, and also the name of the container the codec is often stored in. It'll give you .mp3 files.

  • MP4 is not a codec. MP4 is the name of the MPEG-4 Part 14 container, which can store MPEG-4 Part 2 video (such as XviD), MPEG-4 Part 10 video (such as x264), or MPEG-4 audio in .mp4 files. MPEG-4 audio is called Advanced Audio Coding (AAC) and can also be stored in .m4a – it's just a different extension but the same container.

This is why you can't encode to "MP4" – there's no such audio codec. To understand the difference, please read the following: What is a Codec (e.g. DivX?), and how does it differ from a File Format (e.g. MPG)?

How to encode to AAC audio in MP4:

To encode to AAC audio – without the video at all – you have various options, such as the built-in AAC encoder:

ffmpeg -i a.flv -c:a aac -strict -2 -vn aa.m4a

You have to include the -vn option because FFmpeg will assume with an MP4 container you want both audio and video streams encoded. -vn disables video encoding.

If you want video along with the audio, simply remove the -vn option and choose .mp4 as an extension again. FFmpeg will now use libx264 to encode the video.

How to control the quality

To control the output quality, use -b:a to supply a bitrate, e.g. -b:a 192k.

How to get a list of codecs:

Finally, to find out what codecs FFmpeg can decode (D) or encode (E):

ffmpeg -codecs

And to find out the containers FFmpeg can read (D) or write (E):

ffmpeg -formats

* In your exact case, only libvo_aacenc is enabled, libfaac is not. This is because it wasn't compiled with your static Windows build.

Community
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slhck
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  • why some of ffmpeg output is not catch by pipe? (see `edit 1`) – hugemeow Oct 15 '12 at 10:08
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    FFmpeg writes to `stderr` for whatever reason – you have to redirect output with `ffmpeg -formats 2>1 | …` or `ffmpeg -formats 2>&1 | …` depending on what you want. – slhck Oct 15 '12 at 10:25
  • why it don't write to stdout rather than stderr, i don't think this is kind of error information... – hugemeow Oct 15 '12 at 10:37
  • 1
    Don't ask me why, I have no idea :) Of course it'd make sense to print everything to `stdout` instead. – slhck Oct 15 '12 at 10:44
  • why you choose m4a extension rather than mp4 extension? seems if -vn option is used, i cannot get the video parts, where can i find the detailed description of options such as -vn? btw, why i cannot use libfaac codec? see edit2 :) – hugemeow Oct 15 '12 at 11:14
  • I assumed that because you converted the video to an MP3 audio file, you didn't want video output at all. This is why I suggested using `m4a` and discarding the video output entirely `-vn`. [`-vn`](http://ffmpeg.org/ffmpeg.html#Video-Options) is documented on the FFmpeg website. You cannot use `libfaac` because it wasn't compiled with your Windows static build. You'd have to compile it in yourself, but I don't know how that works on Windows – seems a little complicated. – slhck Oct 15 '12 at 11:24
  • If ffmpeg sent its human-readable messages to `stdout`, it would get in the way of piping the encoder output to other applications. – evilsoup Dec 18 '12 at 09:19
  • @evilsoup Well, yeah, but you could also use a different syntax for *that* use case of course, i.e. have a switch that enables encoding to stdout. Just a design choice. Me personally, I've never had to pipe the actual encoder output via stdout/stdin. – slhck Dec 18 '12 at 09:21
  • @slhck oh, I'm sure there are better ways of doing it (though really, anything much more than bash is beyond me), but piping the output of ffmpeg does have its uses... like piping to neroAacEnc, since ffmpeg's AAC encoders are not the best... actually, I'll put that in an answer here, the questioner might find it useful. – evilsoup Dec 19 '12 at 14:16
  • Oh, one more thing: ffmpeg can internally send stderr straight to stdin with `pipe:2`, like so: `ffmpeg -i input pipe:2`, no need to make the shell do it. – evilsoup Dec 19 '12 at 15:09