[FFmpeg-user] Transcode live mp3 stream to CBR aac+ with ffmpeg

[Chip]

Hi

First time posting.

I'm currently using liquidsoap to transcode a live MP3 stream to a
lower bitrate AAC+ stream. However the AAC+ stream is not suitable
because it is VBR and we require CBR. There appears to be no way to
set CBR within liquidsoap. The input MP3 stream is CBR.

I am therefore now trying to accomplish this with ffmpeg. I am running
Debian version 7.8 and ffmpeg version below:

ffmpeg version 1.0.10 Copyright (c) 2000-2014 the FFmpeg developers
  built on Jul 25 2014 07:50:40 with gcc 4.7 (Debian 4.7.2-5)
  configuration: --prefix=/usr --extra-cflags='-g -O2
-fstack-protector --param=ssp-buffer-size=4 -Wformat
-Werror=format-security ' --extra-ldflags='-Wl,-z,relro' --cc='ccache
cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-nonfree
--enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid
--enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264
--enable-libspeex --enable-nonfree --disable-stripping --enable-libvpx
--enable-libschroedinger --disable-encoder=libschroedinger
--enable-version3 --enable-libopenjpeg --enable-librtmp
--enable-avfilter --enable-libfreetype --enable-libvo-aacenc
--disable-decoder=amrnb --enable-libvo-amrwbenc --enable-libaacplus
--libdir=/usr/lib/x86_64-linux-gnu --disable-vda --enable-libbluray
--enable-libcdio --enable-gnutls --enable-frei0r --enable-openssl
--enable-libass --enable-libopus --enable-fontconfig
--enable-libfdk-aac --enable-libdc1394 --disable-altivec --dis
libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100

I have tried various combinations of commands and I think this gets me
closest - stream details amended to protect the guilty:

/usr/bin/ffmpeg -re -user-agent 42 -i
http://example1.com:8002/stream.mp3 -c:a libfaac -ar 44100 -ab 48k
-acodec copy http://username:password@example2.com:8099/stream.aac -v
debug

The output of the above gives me the following:

user at machine:~# /usr/bin/ffmpeg -re -user-agent 42 -i
http://example1.com:8002/stream.mp3 -c:a libfaac -ar 44100 -ab 48k
-acodec copy http://username:password@example2.com:8099/stream.aac -v
debug
ffmpeg version 1.0.10 Copyright (c) 2000-2014 the FFmpeg developers
  built on Jul 25 2014 07:50:40 with gcc 4.7 (Debian 4.7.2-5)
  configuration: --prefix=/usr --extra-cflags='-g -O2
-fstack-protector --param=ssp-buffer-size=4 -Wformat
-Werror=format-security ' --extra-ldflags='-Wl,-z,relro' --cc='ccache
cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-nonfree
--enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid
--enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264
--enable-libspeex --enable-nonfree --disable-stripping --enable-libvpx
--enable-libschroedinger --disable-encoder=libschroedinger
--enable-version3 --enable-libopenjpeg --enable-librtmp
--enable-avfilter --enable-libfreetype --enable-libvo-aacenc
--disable-decoder=amrnb --enable-libvo-amrwbenc --enable-libaacplus
--libdir=/usr/lib/x86_64-linux-gnu --disable-vda --enable-libbluray
--enable-libcdio --enable-gnutls --enable-frei0r --enable-openssl
--enable-libass --enable-libopus --enable-fontconfig
--enable-libfdk-aac --enable-libdc1394 --disable-altivec --dis
libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[mp3 @ 0x134ee20] Format mp3 probed with size=131072 and score=50
[mp3 @ 0x134ee20] File position before avformat_find_stream_info() is 0
[mp3 @ 0x1358720] Header missing
[mp3 @ 0x134ee20] max_analyze_duration 5000000 reached at 5015510
[mp3 @ 0x134ee20] Estimating duration from bitrate, this may be inaccurate
[mp3 @ 0x134ee20] File position after avformat_find_stream_info() is 81920
Input #0, mp3, from 'http://example1.com:8002/stream.mp3':
  Duration: N/A, start: 0.000000, bitrate: 128 kb/s
    Stream #0:0, 194, 1/14112000: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
Output #0, adts, to
'http://username:password@example2.com:8099/stream.aac -v debug':
  Metadata:
    encoder         : Lavf54.29.104
    Stream #0:0, 0, 1/90000: Audio: mp3, 44100 Hz, stereo, 128 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help

But no ffmpeg process is running and consequently no transcoded stream
is available.

Any suggestions. All help gratefully received.

Best regards

Chip Scooter