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



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

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

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.

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.

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/.




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