MP3 muxer should support writing Xing header for all MP3 sample rates.

[bat_guano]

When converting to MPEG-2 layer III and MPEG-2.5 layer III FFmpeg gives error report "Unsupported sample rate".
FFmpeg does the conversion OK but it reports "Unsupported sample rate".
I've discussed this on the FFmpeg-users mailing list.
Here:- ​http://ffmpeg-users.933282.n4.nabble.com/When-encoding-mp3-at-low-bitrate-FFmpeg-gives-error-report-td4410167.html

ffmpeg -i foo.flac -c:a libmp3lame -b:a 16k -ar 22050 -ac 1 foo.mp3
ffmpeg version N-37961-gf649247 Copyright (c) 2000-2012 the FFmpeg developers

built on Feb 18 2012 00:14:51 with gcc 4.5.2
configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-x11grab --disable-encoder=vorbis --enable-libvo-amrwbenc --enable-libvo-aacenc --enable-libspeex
libavutil 51. 39.100 / 51. 39.100
libavcodec 54. 3.100 / 54. 3.100
libavformat 54. 1.100 / 54. 1.100
libavdevice 53. 4.100 / 53. 4.100
libavfilter 2. 62.101 / 2. 62.101
libswscale 2. 1.100 / 2. 1.100
libswresample 0. 6.100 / 0. 6.100
libpostproc 52. 0.100 / 52. 0.100

[flac @ 0x9723ac0] max_analyze_duration 5000000 reached at 5015510
[flac @ 0x9723ac0] Estimating duration from bitrate, this may be inaccurate
Input #0, flac, from 'foo.flac':

Duration: N/A, bitrate: N/A

Stream #0:0: Audio: flac, 44100 Hz, stereo, s16

[mp3 @ 0x9777d40] Unsupported sample rate.
Output #0, mp3, to 'foo.mp3':

Metadata:

TSSE : Lavf54.1.100
Stream #0:0: Audio: mp3, 22050 Hz, 1 channels, s16, 16 kb/s

Stream mapping:

Stream #0:0 -> #0:0 (flac -> libmp3lame)

Press [q] to stop, ? for help
size= 201kB time=00:01:42.81 bitrate= 16.0kbits/s
video:0kB audio:201kB global headers:0kB muxing overhead 0.016534%

[Elon Musk]

actually this is our muxer bug.

[reimar]

The warning has been clarified. This is not an error but only a warning that means no Xing header has been written (which I personally don't consider much of a loss).
I change this to an enhancement request.

[Carl Eugen Hoyos]

Is this still reproducible?

[bat_guano]

Replying to cehoyos:

Is this still reproducible?

Hi
No, it's not reproducible now.
The "Unsupported sample rate" error message has gone. ;-)

Looks like it has been fixed in git.
Somewhere between
ffmpeg version N-39759-ge9dc616 built on Apr 13
and
ffmpeg version git-2012-05-16-e556121 built on May 16

@xubuntu:~/Desktop$ ffmpeg -i foo.flac -c:a libmp3lame -b:a 16k -ar 22050 -ac 1 foo.mp3
ffmpeg version git-2012-05-16-e556121 Copyright (c) 2000-2012 the FFmpeg developers

built on May 16 2012 17:05:11 with gcc 4.6.3
configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-version3 --enable-x11grab
libavutil 51. 53.100 / 51. 53.100
libavcodec 54. 21.101 / 54. 21.101
libavformat 54. 5.100 / 54. 5.100
libavdevice 53. 4.100 / 53. 4.100
libavfilter 2. 74.100 / 2. 74.100
libswscale 2. 1.100 / 2. 1.100
libswresample 0. 11.100 / 0. 11.100
libpostproc 52. 0.100 / 52. 0.100

[flac @ 0xa81e3e0] max_analyze_duration 5000000 reached at 5015510
Input #0, flac, from 'foo.flac':

Metadata:

ENCODER : Lavf54.3.100

Duration: 00:01:58.89, bitrate: 927 kb/s

Stream #0:0: Audio: flac, 44100 Hz, stereo, s16

[libmp3lame @ 0xa859200] channel_layout not specified
Guessed Channel Layout for Output Stream #0.0 : mono
Output #0, mp3, to 'foo.mp3':

Metadata:

TSSE : Lavf54.5.100
Stream #0:0: Audio: mp3, 22050 Hz, mono, s16, 16 kb/s

Stream mapping:

Stream #0:0 -> #0:0 (flac -> libmp3lame)

Press [q] to stop, ? for help
size= 233kB time=00:01:58.91 bitrate= 16.0kbits/s
video:0kB audio:232kB global headers:0kB muxing overhead 0.068930%

[Carl Eugen Hoyos]

Thank you for clarifying!