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)
The same hiss is heard if the mp4 file is processed by DeVeDe or tovid, I imagine they are using avconv/ffmpeg under the hood.