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[Colin Law <945482@xxxxxxxxxxxxxxxxxx>]

The problem is no longer seen with up to date 14.04 or 15.04

** Changed in: libav (Ubuntu)
       Status: Incomplete => Fix Released

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https://bugs.launchpad.net/bugs/945482

Title:
  Loud hiss on audio converting mp4 to mpg with avconv or ffmpeg

Status in the libav multimedia framework:
  New
Status in libav package in Ubuntu:
  Fix Released

Bug description:
  Using avconv on up to date Precise.
  Converting mp4 (downloaded using get-iplayer but I don't know whether this is significant) using the command
  avconv -i test.mp4 -target pal-dvd test.mpg
  yields a file with audio that is mostly hiss, with an undercurrent of the audio underneath.  The terminal o/p is:

  $ avconv -i test.mp4 -target pal-dvd test.mpg
  avconv version 0.8-4:0.8-1ubuntu2, Copyright (c) 2000-2011 the Libav developers
    built on Feb  9 2012 08:21:31 with gcc 4.6.2
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x9a54260] multiple edit list entries, a/v desync might occur, patch welcome
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.mp4':
    Metadata:
      major_brand     : isom
      minor_version   : 512
      compatible_brands: isomiso2avc1mp41
      encoder         : Lavf53.20.0
      media_type      : 10
      copyright       : � 2012 British Broadcasting Corporation, all rights reserved
      title           : Rugged Wales
      artist          : BBC One
      album_artist    : BBC TV
      album           : Rugged Wales
      composer        : BBC iPlayer
      genre           : Factual
      comment         : Iolo Williams explores some of the best wild and industrial landscapes in Wales.
      date            : 2012-03-01T20:00:00Z
      description     : Iolo Williams explores some of the best wild and industrial landscapes in Wales.
      show            : Rugged Wales
      episode_id      : b01cywyz
      network         : BBC One
    Duration: 00:58:58.16, start: 0.000000, bitrate: 1502 kb/s
      Stream #0.0(und): Video: h264 (Main), yuv420p, 832x468 [PAR 117:117 DAR 16:9], 1401 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc
      Stream #0.1(und): Audio: aac, 48000 Hz, stereo, s16, 94 kb/s
  [buffer @ 0x9a59f00] w:832 h:468 pixfmt:yuv420p
  [scale @ 0x9a59d60] w:832 h:468 fmt:yuv420p -> w:720 h:576 fmt:yuv420p flags:0x4
  Incompatible sample format 's16' for codec 'ac3', auto-selecting format 'flt'                           <----- possibly significant  ---------|
  Output #0, dvd, to 'test.mpg':
    Metadata:
      major_brand     : isom
      minor_version   : 512
      compatible_brands: isomiso2avc1mp41
      network         : BBC One
      media_type      : 10
      copyright       : � 2012 British Broadcasting Corporation, all rights reserved
      title           : Rugged Wales
      artist          : BBC One
      album_artist    : BBC TV
      album           : Rugged Wales
      composer        : BBC iPlayer
      genre           : Factual
      comment         : Iolo Williams explores some of the best wild and industrial landscapes in Wales.
      date            : 2012-03-01T20:00:00Z
      description     : Iolo Williams explores some of the best wild and industrial landscapes in Wales.
      show            : Rugged Wales
      episode_id      : b01cywyz
      encoder         : Lavf53.20.0
      Stream #0.0(und): Video: mpeg2video, yuv420p, 720x576 [PAR 64:45 DAR 16:9], q=2-31, 6000 kb/s, 90k tbn, 25 tbc
      Stream #0.1(und): Audio: ac3, 48000 Hz, stereo, flt, 448 kb/s
  Stream mapping:
    Stream #0:0 -> #0:0 (h264 -> mpeg2video)
    Stream #0:1 -> #0:1 (aac -> ac3)
  Press ctrl-c to stop encoding
  Input stream #0:1 frame changed from rate:48000 fmt:s16 ch:2 to rate:48000 fmt:flt ch:2
  [mpeg2video @ 0x9a57420] rc buffer underflow
  ^Cframe=  123 fps= 32 q=2.0 Lsize=    2360kB time=4.74 bitrate=4082.2kbits/s dup=4 drop=0    
  video:2042kB audio:259kB global headers:0kB muxing overhead 2.574681%
  Received signal 2: terminating.

  If I add the option -acodec ac3_fixed then the sound is ok, so
  possibly it is a problem with ac3 codec.

  The problem is not seen on an earlier version of ffmpeg.

  I can provide a sample mp4 file showing the problem if necessary.

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: libav-tools 4:0.8-1ubuntu2
  ProcVersionSignature: Ubuntu 3.2.0-17.27-generic 3.2.6
  Uname: Linux 3.2.0-17-generic i686
  ApportVersion: 1.94-0ubuntu1
  Architecture: i386
  Date: Sat Mar  3 09:43:31 2012
  InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20111129.1)
  ProcEnviron:
   LANGUAGE=en_GB:en
   TERM=xterm
   PATH=(custom, user)
   LANG=en_GB.UTF-8
   SHELL=/bin/bash
  SourcePackage: libav
  UpgradeStatus: No upgrade log present (probably fresh install)

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