[mdlug] Ffmpeg Problem

[Frank Peters]

Hello,

I downloaded a video from which I need to extract the audio portion.
(The video is actually an audio track with some accompanying images
so this operation is more like stripping the video from the audio.)

Mplayer is able to play the video (and audio) without problem and it
identifies the video stream as h264 and the audio stream as aac.
Therefore, I thought, it should be a simple matter to extract the
audio portion using ffmpeg:

ffmpeg -i input.mp4 -vn -acodec copy output.aac

However, the extracted audio file, which should be a bona fide AAC
audio file, fails to play with mplayer.  (See below for full error
output.)  

I use the above ffmpeg command to extract AAC audio from other MP4
files and have never had a problem before.

Using the file command to determine the file type of output.aac
gives this information:

output.aac: MPEG ADTS, AAC, v4 LC, 44.1 kHz, stereo

This is the same information I get using a ffmpeg extracted AAC
audio file that *does* play with mplayer.

If anyone can shed some light on this problem or offer a different
way to extract the AAC audio, I would be extremely grateful.

Because the mplayer error message is so long, I include it at the
end.

F Peters

mplayer output.aac

Playing output.aac.
libavformat version 55.33.100 (external)
MPEG-PES file format detected.
MPEG: FATAL: EOF while searching for sequence header.
Video: Cannot read properties.
Load subtitles in ./
==========================================================================
Opening audio decoder: [mpg123] MPEG 1.0/2.0/2.5 layers I, II, III
mpg123 init error: Error reading the stream. (code 18)
ADecoder init failed :(
ADecoder init failed :(
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
libavcodec version 55.52.102 (external)
Unknown/missing audio format -> no sound
ADecoder init failed :(
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
Unknown/missing audio format -> no sound
ADecoder init failed :(
Opening audio decoder: [libmad] libmad mpeg audio decoder
Cannot sync MAD frame
ADecoder init failed :(
ADecoder init failed :(
Opening audio decoder: [hwmpa] MPEG audio pass-through (fake decoder)
Cannot sync MPA frame: 0
ADecoder init failed :(
ADecoder init failed :(
Opening audio decoder: [spdif] libavformat/spdifenc audio pass-through decoder.
AUDIO: 48000 Hz, 2 ch, mpeg2, 768.0 kbit/50.00% (ratio: 96000->192000)
Selected audio codec: [spdifmpa] afm: spdif (libavformat/spdifenc MPEG AUDIO BC pass-through decoder)
==========================================================================
[AO_ALSA] Format mpeg2 is not supported by hardware, trying default.
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
[format] Sample format big-endian MPEG-2 not yet supported 
[libaf] Reinitialization did not work, audio filter 'format' returned error code -2
[libaf] Unable to setup filter system can not meet sound-card demands, please send a bug report. 
Couldn't find matching filter/ao format!
Audio: no sound
Video: no video