Bug#736088: libavcodec54: file command reports wrong bitrate on mp3 file encoded by libav

[Reinhard Tartler]

Also note that avprobe does report the "correct" bitrate:

avprobe version 0.8.9-6:0.8.9-0ubuntu0.13.04.1, Copyright (c)
2007-2013 the Libav developers
  built on Nov  9 2013 19:09:48 with gcc 4.7.3
Input #0, mp3, from 'noise_avconv.mp3':
  Metadata:
    encoder         : Lavf53.21.1
  Duration: 00:00:05.04, start: 0.000000, bitrate: 320 kb/s
    Stream #0.0: Audio: mp3, 48000 Hz, mono, s16, 320 kb/s

best,
Reinhard