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

[Bryan Clingman]

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
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

-- 
Bryan Clingman

-------------- next part --------------
A non-text attachment was scrubbed...
Name: transcode.patch
Type: text/x-patch
Size: 4898 bytes
Desc: not available
URL: <http://mythtv.org/pipermail/mythtv-users/attachments/20101230/6d24ddfe/attachment.bin>