[mythtv-users] trandcoding messes up 6 channel audio slow audio playback

[Alan Anderson]

Thanks for the patch.  Its been several years since I compiled mythtv from the 
sources.  But I may have to give it a go.

Has this been reported as an official bug?  If not I would be happy to do so.  

For now I replaced the mythtranscode in mythtvsetup with /bin/true.  Keeps the 
transcoding from being done and does not keep the jobs building in the queue.




On Thursday, December 30, 2010 05:51:46 pm Bryan Clingman wrote:
> On Thu, 2010-12-30 at 09:43 -0700, Alan Anderson wrote:
> > HI
> > 
> > Since upgrading to mythtv 0.24 the transcoding of any show with 6 channel
> > audio ends up with slow audio playback.  Playback before transcoding is
> > fine, after transcoding the sound runs half speed.  Some threads here
> > claim it is a Alsa issue.  But playback before transcoding is fine.  If
> > I copy the nuv file over to another system and use vlc or mplayer the
> > sound is still slow.
> > 
> > I have atrpms mythtv rpm 0.24-256.fc13.x86_64 on the backend
> > 
> > AMD Athlon(tm) 64 X2 Dual Core Processor 4200+  incase its some weird CPU
> > related issue floating point.
> > 
> > I see 0.24-258 is avaialble so I'll update to that.
> 
> I have (had) the same issue.  It's a bug in mythtranscode.  The audio is
> actually 1/3 speed because the 6 channels get cut down to 2.
> 
> It's the same problem discussed here:
> 
> http://www.mythtvtalk.com/playback-half-speed-after-transcoding-13472/
> 
> and several times on this list (including myself)
> 
> Anyway, the patch is attached.  This works by making the audio as
> follows:
> 
> left_transcoded = left/2 + center/2;
> right_transcoded = right/2 + center/2;
> 
> The patch is an UGLY hack, but it works for the short term.  Hopefully
> at some point the AC3 stream can just be copied to the transcoded file.
> 
> > I see the following error in the log file.
> > 
> > 2010-12-27 20:31:18.596 Transcoding from
> > /video/recordings/3111_20101227200000.mpg to
> > /video/recordings/3111_20101227200000.mpg.tmp
> > 2010-12-27 20:31:18.887 MythCoreContext: Connecting to backend server:
> > 192.168.123.20:6543 (try 1 of 1)
> > 2010-12-27 20:31:18.932 Using protocol version 63
> > 2010-12-27 20:31:18.965 MainServer::ANN Playback
> > 2010-12-27 20:31:19.007 adding: pvr.home.lan as a client (events: 0)
> > 2010-12-27 20:31:19.042 MainServer::ANN Monitor
> > 2010-12-27 20:31:19.073 adding: pvr.home.lan as a client (events: 1)
> > 2010-12-27 20:31:21.369 AFD: Opened codec 0x1ecb8f0, id(MPEG2VIDEO)
> > type(Video)
> > 2010-12-27 20:31:21.400 AFD: codec AC3 has 6 channels
> > 2010-12-27 20:31:21.435 AFD: Opened codec 0x1ecc8d0, id(AC3) type(Audio)
> > 2010-12-27 20:31:21.466 AudioOutput Error: Invalid channel count 6
> > 2010-12-27 20:31:21.526 AudioOutput Error: Invalid channel count 6
> > 2010-12-27 20:31:21.558 Found video height of 1088.  This is unusual and
> > more than likely the video is actually 1080 so mythtranscode will treat
> > it as such. 2010-12-27 20:31:21.594 New DB connection, total: 2
> > 
> > Two chanel sound is not a problemn.  Only 6 channel.
> > 
> > I tried to set the transcode option form mp3 to uncompressed it did not
> > help.
> > 
> > So is therea suggested adjustment for this or do I need to just turn off
> > transcoding?
> > 
> > 
> > Thanks
> > Alan Anderson
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