[mythtv-users] Correcting high-pitched ("Chipmunks") audio

Rod Smith mythtv at rodsbooks.com
Mon Aug 4 20:08:54 UTC 2008


On Monday 04 August 2008 09:11:50 am Nick Morrott wrote:
> On 04/08/2008, Rod Smith <mythtv at rodsbooks.com> wrote:
> > Hi,
> >
> >  There's a problem that's been annoying me with some video files obtained
> > on the Internet lately: Some (but by no means all) of these files have
> > audio that's too high-pitched, resulting in "Chipmunks" voices. The audio
> > is in sync with the picture, but peoples' voices are just off. For some
> > characters (particularly men with deep voices), this is quite
> > distracting. This occurs when playing under MythTV's built-in player,
> > mplayer, xine, and every other player I've tried (including QuickTime
> > under Mac OS X). Here are some of the potentially relevant lines from
> > midentify:
> >
> >  ID_VIDEO_FORMAT=XVID
> >  ID_VIDEO_FPS=23.976
> >  ID_AUDIO_FORMAT=8192
> >  ID_AUDIO_BITRATE=192000
> >  ID_AUDIO_RATE=0
> >  ID_AUDIO_NCH=0
> >  ID_VIDEO_CODEC=ffodivx
> >  ID_AUDIO_BITRATE=192000
> >  ID_AUDIO_RATE=48000
> >  ID_AUDIO_NCH=2
> >  ID_AUDIO_CODEC=a52
>
> Assuming the files really do have good audio - are there /any/ systems
> that play the file(s) normally? Have you tried Media Player Classic on
> Windows for example, with a suitable AC3 codec installed?

I haven't tried Windows (I've no Windows systems set up for this sort of 
playback), but I have the same problem with these files on three Linux 
systems, one of which dual-boots to Mac OS X. Thus, I'm pretty sure the files 
are foobared rather than this being a driver or codec issue. Hence my asking 
if there's a way to fix the audio in transcoding (or by extracting the audio, 
converting it in some way, and then re-combining the files).

> The audio is listed as being a52 (Dolby Digital) which could cause
> playback problems if you are running your audio at something other
> than 48kHz and the audio is being rate-converted on-the-fly. Do you
> have digital audio passthrough configured in mythfrontend setup? Does
> extra verbose logging in mythfrontend show any useful audio messages?

I have no problems playing other audio files with 44.1kHz or 48kHz audio. It's 
a problem with just a handful of files.

-- 
Rod Smith


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