[linux-dvb] Re: Mplex doesn't work

[Henning Holtschneider <hh@holtschneider.com>]

On Sun, 3 Jun 2001, Carsten Koch wrote:

>    V1a V1b V1c V1d A1 V2a V2b     V2d A2  ....
>
> ?
>
> That sounds like a reasonable explanation to me.

I'm no MPEG or DVB expert, but that's how I have understood the DVB
broadcast mechanism. After all, it's very likelike in a digital broadcast
environment that some of the data will get lost on the way and you cannot
show what isn't there.

> I would assume that in the above situation we really see
>
>    V1a V1b V1c V1d A1 V2a V2b V2b V2d A2  ....
>                               ^^^
> When we are watching the program "live"?

Remember this is MPEG, so V2b isn't replicated - it's just dropped. If V2b
is an I-frame (full image), you will see the old image being "washed away"
by the new picture (because the following P- and B-frames won't fit to the
I-frame the MPEG decoder refers to). If it's a P- or B-frame, you will
only see a small image distortion. [P.S. experts, please correct me if
this is rubbish ...]

> So I guess there are three ways to fix this:
> [...]

Everything is fine as long as you replay the PES stream with a decoder
that known how to properly deal with it. Again: I don't think this is a
problem with VDR and the a/v drifting has been discussed here before. It's
just that nobody as come up with a solution so far (i.e. modified version
of mplex that inserts silence or drops video data) and I would like to get
enough knowledge to change that ;-> It can't be impossible because
PVAStrument (http://www.offeryn.de/dv.htm#pvas) does exactly what is
needed (and it now even takes VDR's files as input).

Regards,
hh



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