Problème FFMPEG flv = > avi

Bonjour,

Je propose via une application flash d'enregistrer un message avec sa webcam donc je récupère sur mon serveur un fichier FLV.
Delà, j'ai installé ffmpeg pour qu'il encode ensuite mon fichier en "avi".

Mais marche pas....
Mon fichier "avi" est créé mais 0 octets.

Je vous mets la sortie de ma ligne de commande.

root@xxxxxxxxxx:~# ffmpeg -i "fichier.flv" -s 480x320 "fichier.avi"
ffmpeg version 0.8.6-6:0.8.6-1, Copyright (c) 2000-2013 the Libav developers
  built on Mar 24 2013 18:40:26 with gcc 4.7.2
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a future release. Please use avconv instead.
[flv @ 0x6421e0] decoding for stream 1 failed
[flv @ 0x6421e0] Estimating duration from bitrate, this may be inaccurate
Input #0, flv, from 'fichier.flv':
  Metadata:
    canSeekToEnd    : true
  Duration: 00:00:03.02, start: 0.000000, bitrate: N/A
    Stream #0.0: Video: flv, yuv420p, 160x120, 1k tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: [0][0][0][0] / 0x0000, 0 channels
[buffer @ 0x646660] w:160 h:120 pixfmt:yuv420p
[scale @ 0x644d20] w:160 h:120 fmt:yuv420p -> w:480 h:320 fmt:yuv420p flags:0x4
[libmp3lame @ 0x641b80] Requested sampling rate unsupported using closest supported (8000)
Incompatible sample format '(null)' for codec 'libmp3lame', auto-selecting format 's16'
Output #0, avi, to 'fichier.avi':
    Stream #0.0: Video: mpeg4, yuv420p, 480x320, q=2-31, 200 kb/s, 90k tbn, 1k tbc
    Stream #0.1: Audio: libmp3lame, 8000 Hz, 0 channels, s16, 200 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Decoder (codec id 0) not found for input stream #0.1

J'ai apprement 2 trucs qui vont pas:

[libmp3lame @ 0x641b80] Requested sampling rate unsupported using closest supported (8000)
Incompatible sample format '(null)' for codec 'libmp3lame', auto-selecting format 's16'

Decoder (codec id 0) not found for input stream #0.1

Merci de votre aide.