[linux-dvb] Re: Alternative v4 demux API

[Holger Waechtler <holger@convergence.de>]

Michael Hunold wrote:
> Please refer to the fundamental difference I desribed in my mail to Ralph:
>
> Different demux devices with included filter capabilities suggest to the 
> user that there's hardware behind it. This is currently not the case for 
> any hardware out there.
It is. Whenever we implemented multiple demux devices for an adapter 
each of them stands for an independent demux channel for which you can 
select stream source and ouput independently from the other ones.

> The "demuxes" are input selectors and filters 
> are shared.
no. If you have an second or third demux device (which means that you 
have 2 or 3 seperate demux channels) it's input selector and filters are 
independent from the first one.

> So it should be possible to open a *filter* as many times as 
> there are h/w filters available, not a "demux" device, where the filters 
> are shared betwenn all "demuxes".
Isn't this the case?

Basically the API right now was intended like this:

Imagine you have 2 frontends, 3 demux channels and 2 MPEG decoders on 
your DVB chipset. This means that you have the following DVB devices:

/dev/dvb/adapter0/frontend0
/dev/dvb/adapter0/frontend1
/dev/dvb/adapter0/demux0
/dev/dvb/adapter0/demux1
/dev/dvb/adapter0/demux2
/dev/dvb/adapter0/video0
/dev/dvb/adapter0/video1
/dev/dvb/adapter0/audio0
/dev/dvb/adapter0/audio1

Now you could use the first channel connected to the first frontend and 
the first MPEG decoder to watch Live-TV.

The second one is connected to the second frontend and outputs packets 
to memory or indirectly to disk for recording.

The Third one is feeded from disk/memory and outputs the stream to the 
second MPEG decoder.

So you can implement recording/timeshifting with simultanous 
picture-in-picture control of the program received from the first 
frontend. Or implement MHP applets which use one of the MPEG decoders to 
decode I-frames or Streamlets for background images while you still 
decode the TV picture into a small PiP on the right upper corner. And 
record a third program to the disk while you're doing all this.

You can do so since you can route streams of the 3 demux channels 
independently and can select input/output for each independently.

Holger



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