[linux-dvb] recording multiple channels

Johannes Stezenbach js at linuxtv.org
Wed Apr 20 20:27:31 CEST 2005

Matt Lovett wrote:
> I understand (thanks to the recent posts on the list) that it is
> possible to record multiple programs at once, so long as they are on
> the same multiplex. My question is, how do I do that using the DVB
> api?

The design of the recording API is somewaht limited. The V4 API
supports recording filters which would let you do what you
want in a simpler way (and also using rec hw support on STB chips).

> If I want to record a single programme (collection of PIDs) then I can
> filter them to TS_OUT_TS_TAP, and the pids will be automatically mixed
> into a new TS that I can read from the dvr device.
> I'm guessing if I try that with multiple channels (2 collections of
> PIDs) then I'd get a TS with both channels in it, and I'd have to do
> work to separate the two.

Yes, a simple PID filtering step is required.

> One way would be to do the above, and write it out as 2 streams
> (filter each packet one way or the other, and rewrite the PMT etc as I
> go - sending a PMT into each stream). If I do that, which parts of the
> stream would I need to rewrite?

I'd create a new PAT and PMT from scatch with just the minimum
possible content.

> Another approach would be to us TS_OUT_TAP, and do all the
> remultiplexing myself. Not sure how to go about that... and it sounds
> like if I go the TS_OUT_TS_TAP route then the driver does more work
> for me.

This won't work as TS_OUT_TAP strips the TS headers and adaptaton


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