[mythtv-users] Losing audio on "lossless" transcode

[David Boxall]

On 17/10/2008 at 7:37 PM David Watkins wrote:
>
> ... I haven't managed to find a single
> transcoding profile that will work with all UK Freeview DVB-T
> recordings.  What works for some recordings fails on others.  I
> believe that it's down to the variety of audio and video encoding
> times that are used.
>
 From what I've read, each country has different guidelines for DVB-T.  
Within countries, implementation differs between broadcasters.  A given 
broadcaster won't necessarily use the same implementation for every 
program.  That makes for a difficult environment but, as ProjectX shows, 
not an impossible one.
> ...Are you testing using recordings from the same show or channel?...
>
Different shows, different channels.  On MythTV, always the same 
result:  "lossless" transcode loses the audio.

On 18/10/2008 at 1:36 AM Ian Barton wrote:
> ...
>
> I use mythtranscode and ffmpeg called from a custom python script. This 
> works for most UK DVB stuff. However, mythtranscode fails miserably on 
> some recordings, usually from UK TV History. It complains that it can 
> find any video frames, even thought the recording plays fine.
>
> My court of last resort, which hasn't failed yet, is to demux them using 
> ProjectX and the remux.
>
> Note before doing any other transcoding on DVB recordings you need to 
> rebuild the seektable and do a lossless mpeg->mpeg transcode using 
> mythtranscode, or you will get audio/video sync problems.
>
> The two commands I use are shown below. The %s is a parameter 
> interpreted by the python script.
>
> '/usr/local/bin/mythtranscode --showprogress --honorcutlist --mpeg2 -c 
> %s -s "%s" -o /tmp/%s.tmp'
>
> '/usr/local/bin/mythtranscode --mpeg2 --buildindex  --showprogress 
> --chanid %s  --starttime "%s"'
Thanks for the help.  I clearly have a lot to learn.  Come to think of 
it, so does MythTV if it's to get a credible grip on DVB-T.

-- 
David Boxall                    |  When a distinguished but elderly
                                |  scientist states that something is
                                |  possible, he is almost certainly
                                |  right. When he states that
                                |  something is impossible, he is
                                |  very probably wrong.
                                                   --Arthur C. Clarke