[linux-dvb] Re: Using a low-budget card as a secondary card.

[ma.hoff@bigfoot.com]

> >
> > The only thing I found is the source code of mplex, i.e. the muxing
> > part of bbmpeg, which I used for the mplex program in the mpegtools.
> > As far as I can understand the code, they use a "faked" buffer that
> > represents the buffer of the player. they "write" the PES data into
> > the buffer according to the PTS and check if the PTS is less than the
> > SCR which they also simulate. Then they use some coditions depending
> > on buffer filling and PTS of audio and video to write into the buffer
> > and read out of buffer, i.e. write to disk. They only rule you can
> > make out of this is that you have to have the data out of the buffer
> > before it needs to be displayed, i.e. PTS < SCR. The audio and video
> > buffer size acts are the boundary conditions for that. I didn't have
> > time to take all that stuff apart, so I just used it as is.
> > Maybe theres is a scientific paper or maybe a some kind of thesis
> > about that on the net.
> 
> That sounds not all that promising as mplex does not cover all problems in 
> vdr-files so far - remuxed streams still have vanishing audio (and latency)
> at the same point the original file has.

As far as I understand the problem is that Audio and Video is only in sync when every PTS information provided is used. By demultiplexing you strip off the PTS and by re-multiplexing again you take the seperate audio and video streams as is. Thats why you sometimes got vanishing audio and stuff.
The only way to get a clean and 100% sync mpeg is to have a multiplex routine which checks for ever audio PTS and searchs for the according video PTS and vice versa. I'm not sure if this can be done on the fly...
So for Offline conversion of PVA (PES) Files to mpg I use a great tool names PVAstrumento which in fact does the mux methods described above. You can check this out on http://www.offeryn.com/
Maybe if you contact Wiljo (the Author of PVAstrumento) he is willing to share the code for multiplexing with you. As far as I know he told me once, that this new version of PVAstrumento (2.xx) would have the ability to be integrated as an "on the fly" filter. But of course it's written for windows and must be ported. If you like I can make the "first contact" (maybe watching star trek a little often ?).
btw: I have tried PVAstrumento on some files recorded by VDR and it works - so the format is basically the same...

I hope this helps...

Regards, Martin.




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