[vdr] Re: cAudio Plugin

[Wolfgang Fiesel <fie@iis.fhg.de>]

Hello,

Klaus Schmidinger wrote:

>Robert Schneider wrote:
>  
>
>>Hi all (and especially Klaus, congratulations to the award),
>>    
>>
>
>Thanks :-)
>
>  
>
>>I'm investigating on how a plugin could make use of the cAudio class to
>>process AC3 data and forward it via the dvb-s' internal SPDIF port.
>>
>>So far the Audio class is working and I get the right calls, however I
>>have problems understanding:
>>
>>        a) how I can make vdr prevent sending the regular PCM stream to
>>the card (while replaying a recording)
>>                my understanding is that all registered cAudio classed get
>>called which might lead to multiple audio outputs
>>        b) how I can obtain access to a class (or the device) to write my
>>processed AC3 data to the card
>>                my investigation on the AIO patch show that the processed
>>AC3 data is writton into a cFrame which is then
>>                forwarded via an AudioCallback function
>>
>>Can someone shed some light on this for me?
>>    
>>
>
>AC3 over the DVB card's S/PDIF will most likely be done directly inside
>cDvbDevice, since this is a matter of the DVB device itself.
>See my comment in cDvbDevice::PlayAudio().
>
>I'm not sure yet how switching off the "normal" audio will be done.
>  
>
The trick is here to clear or to remove (distroy) the audio bitstream 
inside the MPEG-2 stream. The audio id is 0xc0. All what we have to do 
is to parse for this element id and to clear the LAYER-2 audio 
bitstream. Afterwards we have to extract the AC-3 data (are located 
inside the private elementary stream ID 0xbd), wrap around the direct 
PCM identification header and add it together with the right time stamp 
info at the MPEG-2 PES stream.
That's all.

Currently I'm fighting with the new plugging structures to understand 
the signal flow. Who will be the first to have this plugging ?

Bye
Wolfi




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