[linux-dvb] Re: Fw: DVB audio/video decoder API

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

Johannes Stezenbach wrote:
> 
> On Thu, Oct 31, 2002 at 05:28:21PM +0200, Dennis Noordsij wrote:
> >
> > > capability... As far as I understand Ralph's work here he found a way
> > > to grab the TS data by directly reaching into the data stream at an earlier
> > > stage, before the PES packets are generated. maybe I'm misunderstanding
> > > something here, but the bottom line is: the driver should _always_ provide
> > > TS data - IMHO...
> >
> > If the TS data CAN be directly grabbed (can someone confirm this?) I agree,
> > but otherwise, maybe not :)
> 
> That's what I mean. If the hardware won't give you TS packets, the
> driver should not try to emulate this. Likewise, if the hardware
> only gives you TS packets, the driver should not repack them into
> PES packets. That's better done in userspace.
> 
> I'm not shure about Ralph's last work for the AV7110 firmware, so maybe
> my knowledge is out of date. I don't know what the firmware does
> for DATA_TS_RECORD.
> Look in av7110.c for pes_to_ts(). AFAIK the does AV7110 not give you
> the TS packets, at least not if the data is also going to the
> MPEG decoder (i.e. maybe it works for DMX_PES_OTHER).
> 
> It would be nice if Ralph or Marcus could enlighten us with their
> opnion on that.
> 
> > If it is not strictly necessary to multiplex a TS stream in software in the
> > driver and then demux it immediately after in the application it
> > significantly lowers the performance requirements for STB controller
> > hardware. While the cheapest available hardware today has no problem doing
> > this anyway, I am also sure that nobody would mind having extra cycles to do
> > other things with, if only to save some power.
> 
> I don't see why an application would request a TS from the driver if the
> applicaton wants PES and the driver can deliver PES.
> STB controllers that support recording can use any format they want,
> as long as they support playback of the same format.

The entire recording and "Transfer Mode" mechanisms of VDR are based on the
assumption that the driver can deliver TS packets, since that's the most
basic form of data (AFAIK that's the way it is broadcast), and it is the
easiest way to distribute the data to various receivers. This is what made,
for instance, "overlapping recordings" possible in VDR. I also don't see
how one would be able to record more than one programme (or one programme
with several audio PIDs) if the driver delivers PES. As far as I understand
things this is only possible if it delivers TS (but please correct me if I'm
wrong here).

Klaus
-- 
_______________________________________________________________

Klaus Schmidinger                       Phone: +49-8635-6989-10
CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
Hofmark 2                               Email:   kls@cadsoft.de
D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
_______________________________________________________________


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