[linux-dvb] Re: Problems using mplex

[ma.hoff@bigfoot.com]

> The synching part of the firmware takes the audio and video PTS and if
> the gap is too large it skips or delays a frame. So the above wouldn't
> matter.
But only for playback, right ?
For recording we get the unfiltered stream, right ?
 
> Are there specific transponders that have the problem, or certain
> types of programs? 
Most problems I have on SAT1 (where I always use to record STAR TREK) and sometimes on Pro7, but rather seldom !
RTL seems to be rather clean ;-)
Sorry, I don't know which transponder they belong to at the moment...

> I already knew what you were talking about, I just didn't believe that
> anyone would broadcast that way.
Seeing is believing ;-)

> Yes, all the PTS information is thrown away in demuxing, but now I see
> why my attempts to write a remuxer didn't work. At first I was using
> the PTS provided by the original stream and tried to calculate
> additional PTS, but they never matched. Only at the beginnig, but than
> the audio usually began to drift. So I took mplex and thought it would
> make it better. Well, if I had time I would start from scratch and try
> to do it differently, with all the information I have now.
Wouldn't keeping the original PTS information partially solve the problem ?
If the application playing back the result takes care about the PTS it would be in sync - okay only if the buffer it uses is large enough ;-)
This is somehow very un-clean, I know, but as some kind of quick hack it may help ?

Another way i can think of is to change mplex, so that it creates a third file while demuxing which holds the PTS difference information for every packet.
Then it could do a "second pass" changing the audio file according to the PTS-diff file. (dropping packets or adding silence ? - or dropping video packets) Afterwards the "repaired" audio file and the video can be muxed, with new PTS, just like now but with audio_delay=0 and video_delay=0...

Is it possible for you to implement one of those ideas an some kind of quick hacks ?

Because my c knowledge is just copy-and-paste ;-)

But I'm willing to do any test and theoretic help I can provide !
I also have a CYBERHOME DVD Player which plays X-SVCDs with the remuxed DVBs Streams on it - so it's rather ideal for testing (no re-encoding stuff).

Martin.




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