[linux-dvb] Re: FF cards alter PTS'?

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Holger Waechtler wrote:
> 
> Hi Klaus, hi everybody else,
> 
> Klaus Schmidinger wrote:
> > Ralph Metzler wrote:
> >
> >>Johannes Stezenbach writes:
> >> > Ralph Metzler wrote:
> >> > > Johannes Stezenbach writes:
> >> > >
> >> > >  > The av7110 destroys the adaptation fields if you record and watch
> >> > >  > at the same time (record with DMX_PES_OTHER to prevent this). However,
> >> > >  > the DMX_GET_STC should give you correct values. Also, AFAIK the PES
> >> > >  > header is not altered by the av7110 or firmware, so the PTS should
> >> > >
> >> > > Video PES which are being decoded are taken apart. ES and PTS (lower
> >> > > 32 Bit only) go into separate ring buffers.
> >> > >
> >> > >  > be correct. Or maybe the 33rd bit of the STC/PTS gets lost?
> >> > >
> >> > > Yes, for decoded video always.
> >> >
> >> > I thought the TS packets are grabbed from the TPP before they
> >> > reach the decoder? So we should get unaltered PES?
> >>
> >>No, AFAIK, you cannot get all packets of the video PID before they reach
> >>the decoder. The TPP does all the writing into the ES ring buffer by
> >>itself. The only exception seem to be packets with PUSI bit set. They are
> >>parsed by the firmware ROM. It also handles the PTS buffer. Here one
> >>can also find the infamous PTS length counting bug which (indirectly)
> >>caused the "jerking in playback" bug.
> >>But this is all from disassembling the firmware ROM and lots of
> >>guessing. There is no documentation on this.
> >>
> >>Maybe there is a better way to do this. One could do more rewriting in
> >>the EOP FIQ (as I did to get the time shifting working). One
> >>could always handle live viewing like playback, writing to the
> >>decode buffers in software. This would give you the complete video
> >>packets. It would probably also get rid of TPP lockups which seem to
> >>be caused by bad video streams from weak channels or during tuning.
> >>But is it really worth putting more work into this old hardware?
> >>
> >>Ralph
> >
> >
> > Well, AFAICS this "old hardware" is very widely used, and the main
> > platform VDR is designed for. And judging from the download volume
> > every new version of the "linvdr" distribution causes (according to
> > Mirko Dölle) VDR must be rather popular ;-) So I guess this hardware
> > will still be in use for quite a while, and I can see no adequate
> > replacement around - but that may be due to my lack of market
> > overview...
> 
> :) sorry Klaus, there are plenty: Take any of the decoderless
> Nova/Nova-USB/ Skystar2/Avermedia cards, they cost only a fraction of
> the old av7110 based cards.

I wasn't referring to budget cards. I meant a full-featured card, with
TV-out, that is able to receive AND replay. Plus the ability to connect
a CAM to it.

> And every modern PC is able to decoder
> several MPEG streams in software at a time.

But that would require quite a bit more CPU power than my current 450MHz
machine - which means more cooling, more noise...

> Painting OSD bitmaps on the
> YUV overlay is trivial and gives you the freedom to remove all the evil
> hardcoded OSD-related limitations introduced in the VDR source.

The actual device implementation (including the OSD) in VDR can be replaced
through a plugin, like, for instance, the Xine plugin.
So anybody who really wants to use a different hardware for replay
can do so.

> I slowly get the feeling that VDR is might be the only reason that keeps
> those old expensive and misdesigned av711x cards alive, not?

If by "keeping alive" you mean "keeping them on the market", I don't
know. Maybe this is actually true, but then again, where's the
problem? If some manufacturer would sell a better DVB-S card (but
of course _with_ MPEG decoder and tv out) I'd gladly give it a try,
provided the LinuxDVB driver supports it.

> Believe it or not, VDR became a market-driving force with time, all
> these articles in the local computer magazines have been a source of
> publicity that commercial DVB card manufacturers could only dream of.

Well, apparently VDR actually does what most people really like ;-)
It is simple, not bloated and easy to handle.

> > Many people (including myself) have several of these DVB cards and
> > would sure appreciate any improvement that could be done on them
> > (at least in order to make them run more stable and reliable).
> 
> Don't you want to add a software decoder based e.g. on ffmpeg to VDR?
> Take a look in the ffplay.c source code, you can rip out most of the
> code there. And you get HDTV and MPEG4 decoder support for free.

Personally I don't have any need for this, because I still use the TT
DVB-S cards, and since I have quite a few of these I guess I'll be able
to run them for quite a while ;-)

The plugin interface of VDR should be flexible enough to allow the
output device to be replaced by something else (if not, just let me know
and I'll see what I can do in the next version). However, this will
have to be implemented by somebody who actually has the need for
this and wants to run VDR on a platform that doesn't have a TT DVB card.

> Holger
> 
> ffplay.c is the example application of ffmpeg, you find it in the ffmpeg
> CVS on http://ffmpeg.sourceforge.net/. It depends on SDL and ffmpeg
> only, it has been successfully compiled on Linux and various other
> Unices, MacOS X and even been crosscompiled for Windows using mingw32.
> ffmpeg is currently one of the most advanced free software decoders, it
> has been written by Fabrice Bellard - the same guy who also wrote tcc (a
> tiny and really fast one-pass C compiler which can used for scripting,
> almost C99 compliant), qemu (a processor emulator which you can use to
> execute e.g. x86 Linux applications your PowerPC with surprising
> performance) and some other impressing projects. Check out
> http://fabrice.bellard.free.fr/.

Well, somebody should write a plugin that implements such a device, and
you could run VDR without a full featured DVB card. The question would
then be, however, if the budget cards you use then will support CAMs.

Please understand, though, that people aren't just going to throw
away their full featured DVB cards. There are hundreds (or, more likely,
thousands) of VDR systems out there with full featured DVB cards,
running just fine.

Klaus


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