[linux-dvb] Re: V4 API proposal

["Florian Schirmer" <jolt@tuxbox.org>]

Hi,

>The number of demux devices should depend on 
>how many input streams can be handled in parallel.

Right. But even then you can end up in a situation where 2 users try to set
2 demuxes into memory reading mode, but only one memory channel is
supported. In this case the driver is allowed to simply reject the second
DMX_SET_SOURCE call with -EBUSY. If your hardware has 3 inputs but can only
use 2 of them concurrently it doesn't make any sense to provide 3 logical
demuxes. Thanks for outlining this. I will change the proposal.

>I agree that this is a much better approach than using the dvr. But please 
>consider that when doing this we will get a functiuonality that is not 
>demultiplexing. Instead its somehow TS filtering and here we may need
additional 
>functionality that does not fit into the demux. The partial output stream
can 
>consist one or more programs. We also need the filter some tables to 
>get the stream information when doing playback. To have a consistent TS
stream 
>we need to change the PAT and reinsert it into the stream.

I agree that this is more than just demultiplexing. But this is what most of
the hardware is capable of. IMHO playing around with the PAT or any other
information does not belong into the (kernel) demux device. It's up to the
(userspace) application or a (userspace) middleware library to provide such
services (e.g. PAT reinsertion). The STB's i'm aware of can handle these
"broken" PAT's by dooing some bookkeeping about the recorded stream.

>Concerning PS and multiple PES, it also needs to be demuxed. We also need
to set 
>filters based on the streamids, we have timing information similar to STC,
and 
>we also have data that corresponds to tables.  When this is in the same
device 
>the interface will get differnt meanings. If not we will get a TsDemux and
a PsDemux.

I agree that you may need some sort of demuxing here too. But it's is very
different from the demuxing done to the TS data. So you wont get any benefit
from merging the PS demux into the TS demux. That is why i propose to create
an additional device for that. (Even if the driver ends up using the same
hardware as the TS demux would do).

Thanks a lot for your comments.

Bye,
   Florian




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