[Ffmpeg-devel] Mpeg2 audio chirps

[Dan Gelb]

I'm trying to encode an audio file using the Mpeg audio layer 2 codec, however I'm getting some short, high pitched squeaks in the compressed audio. The input audio source is nearly silent, but the output has three short but loud chirps in it. The command line and console output is:

ffmpeg -i sample.wav -ab 256 sample.mp2
Use a real OS!
FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
  configuration:  --enable-memalign-hack 
  libavutil version: 49.0.0
  libavcodec version: 51.9.0
  libavformat version: 50.4.0
  built on Apr 19 2006 09:56:28, gcc: 3.2.3 (mingw special 20030504-1)
Input #0, wav, from 'sample.wav':
  Duration: 00:00:21.1, start: 0.000000, bitrate: 767 kb/s
  Stream #0.0: Audio: pcm_s16le, 48000 Hz, mono, 768 kb/s
Output #0, mp2, to 'sample.mp2':
  Stream #0.0: Audio: mp2, 48000 Hz, mono, 256 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
size=     662kB time=21.2 bitrate= 256.0kbits/s    
video:0kB audio:662kB global headers:0kB muxing overhead 0.000000%

I've uploaded the source audio file here:
ftp://ftp.mplayerhq.hu/MPlayer/incoming/MpegChirp/sample.wav

The compressed version created by FFmpeg is here:
ftp://ftp.mplayerhq.hu/MPlayer/incoming/MpegChirp/sample.mp2

The short chirps are near the 5, 8 and 14 second marks.

The result after converting back to wav is here:
ftp://ftp.mplayerhq.hu/MPlayer/incoming/MpegChirp/sampleout.wav

Dan