[linux-dvb] Re: [RFC] Limitations of current filtering

[Johannes Stezenbach <js@convergence.de>]

On Fri, Dec 05, 2003 at 03:52:32PM +0100, Klaus Schmidinger wrote:
> Holger Waechtler wrote:
> > 
> > ...
> > > At that point dvrY is totally useless and it could be theorically
> > > removed (but it's better to not break existing apps, of course).
> > 
> > We should keep it in v3, in v4 it will vanish anyways. The DVR device is
> > still required for MultiPID-TS filters when we don't implement b).
> 
> I have to admit that (due to lack of time) I didn't follow the
> V4 API discussion, so please forgive this question: if the DVR device
> will vanish, what will an application (like VDR) have to use instead?
> A short link to the relevant doc page or posting would do just fine.

The V4 API provides two kind of PID filters:
- simple PID filters (only one PID per file descriptor), full TS packets
  and payload-only
- recording filters for multiple PIDs (filtered TS)

Both are supported by a wide range of current hardware. The recording
filters can also be emulated in software, but to do this correctly
one needs access to the whole TS, otherwise the filtered TS will have
different muxing than the original TS (no problem for current VDR as
it stores PES packets anyway).

The payload-only PID filters are similar to the current "PES filters"
but the name implies that the driver does not assemble PES packets
or search for packet boundaries. I plan to support multiple filters
for the same PID (I started implementation but did not get very far
yet).

So, VDR would use the V4 recording filters, and would open a new
filter for each recording. The post-demuxing in userspace does
not need to be done anymore. OTOH, the TS playback capability
for the AV7110 cards will be dropped (the current implementation
has too many problems (locking related), and the hardware only
accepts PES for playback). So I guess VDR will keep the PES
recording format.

HTH,
Johannes


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