[linux-dvb] Re: V4 API questions

[Alasdair FARMER <alasdair.farmer@st.com>]

> > 1) The dvb_dmx_decoder_type does not support Audio
>  > descriptor as a type.  A good number of broadcasters
>  > are starting to transmit this and it may have different
>  > decode requirements from a normal audio channel
> 
> I don't understand what an "audio descriptor as a type" 
> means. 8-( Can you specify your problem?
> 

Within a TS there are PIDs for what is called 'Audio Descriptor' data.  This is an audio stream which contains a description of what is happening in a scene for the visually impaired.  This audio data may need to be processed and treated separately from the main audio data and may well need to be decoded/processed in a different way to standard audio data.  'Audio Descriptors' are being adopted by a number of broadcasters and support is being specified as mandatory for a number of new STB's


> > 2) The playback speed seems to be modified from the video
>  > decoder - how is this supposed to modify the audio ?
>  > In many systems the audio is still 'rendered' (within
>  > certain parameters, say up to x2) as the playback speed is 
> adjusted.
> 
> I'd say that audio output is muted if playback speed != 1 (ie. live 
> view), although that I admit that adjusting the playback 
> speed around 1 
> would give cool effects. 8-)

While muting may be the route that some applications want to take, this is not a route appropriate for all applications.  Specifically some CE devices typically support audio playback for trick modes between 50% & 200%.  The problem I have is there is no way to provide synchronisation between audio and video - or am I missing something ?

<snip>

> > 4) What is the naming convention for decoders now that the linkage
> > between decoders and demux's is dynamic ?

> Hm, audio and video mpeg decoders are simply enumerated.

It would be nice if it was possible to ask the demux what the 'attached' decoders were as there is no implicit mapping between demux's and decoders


<snip>

> It sounds as if your have already some special hardware in mind. Does 
> the V4 api suit that?

Well the answer is I guess most of ST Microelectronics STB (& DVD) current and next generation of silicon.  (ST's solutions are present in 80% of STB's worldwide).  We are looking to better support LinuxDVB - but we have to be happy that the API will actually do the job for us.  In general it looks like it probably will (assuming it continues to mature as it has been), I am just digging deeper to check.  The V4 API is the first iteration which is beginning to look like a 'real' API that we could use.

Regards

Ali Farmer.




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