[mythtv-users] Gappy playback of some DVB-T recordings

Justin Hornsby justin.hornsby at gmail.com
Tue Nov 14 19:39:36 UTC 2006


On 14/11/06, Justin Hornsby <justin.hornsby at gmail.com> wrote:
> Hi all.
>
> I'm having problems playing back some DVB-T recordings.
>
> All the recordings I've seen the issue with are from BBC channels in the UK.
>
> My frontend is based on minimyth, running version 0.20-19.  Backend
> can play back the recordings just fine.
>
> With XvMC and deinterlacing enabled (the issue never shows when I
> don't deinterlace), every 20 seconds or so the playback pauses a
> little & I notice a slowdown of playback & hear a gap in the audio.
>
> When timestretch is enabled (1.05x say) I don't get the problem.  When
> deinterlacing isn't enabled (the method doesn't seem to matter), I
> don't get the problem either.
>
> When I use mythfrontend -v playback I see stuff like
>
>  NVP: Video is 5.29265 frames ahead of audio, doubling video frame
> interval to slow down.
>
> .. around the kind of time interval the gaps in audio come about.
>
> mythfrontend -v all shows me lots of messages about so many audio
> buffers being needed when only so many are available, and plenty of
> messages about a broadcast saying they're available.
>
> I've tried every audio buffering setting & playback option possible -
> all with the same result.
>
> My backend can play back all the recordings just fine using nvidia
> xvmc & deinterlacing, so I know it's not the recordings themselves to
> blame - the problem is with the frontend machine somewhere, whether
> that be with drivers, config or mythtv itself.
>
> Does anybody have any ideas what's going on or have anything else I can try?

Little update:

I took a recording which was having this playback problem & removed
its extra audio track with ffmpeg -i foobar.mpg -vcodec copy -acodec
copy outputfile.mpg, rebuilt the seek table with mythcommflag
--rebuild --file outputfil.mpg and hey presto!

The file plays back juuust fine now.

So, perhaps there's something wrong with an mpeg parser somewhere
along the line.

Now does that give anybody any ideas?

Justin
-- 
Justin Hornsby
Moderator of www.mythtvtalk.com and MythTV advocate.
email: justin(dot)hornsby(at)gmail.com
web: http://www.juski.co.uk


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