[linux-dvb] Linux DVB API 4 / Audio API

[Johannes Stezenbach <js@convergence.de>]

Rob.McConnell@Zarlink.Com wrote:
> Johannes Stezenbach <js@convergence.de> wrote: 
> > Audio is difficult, because I don't have a clue. We (== Convergence)
> > currently do mixing via a simple OSS device, and I thought about the
> > possibility of using parts of ALSA for more complex audio post
> > processing options.
> >
> > If we could create an API which works for all of us I would like to include
> > it in the DVB API.
> 
> For audio h/w (e.g. DSP), status information would normally be returned in
> a register or memory location.  I guess
> access to this register would have to be done via a read syscall or we
> could setup an audio event to watch.  OK, we would need to cater for AC-3,
> LPCM, DTS, AAC, OGG, MPEG-1, MPEG-2 (inc. multichannel) and any other audio
> standards.  How do we want to proceed next?

Currently the audio API is very simple:
- we can feed one stream into the audio decoder; possible formats
  include PCM, MPEG-Audio, AC3, AAC etc.
- we take care of syncing audio to video (or to the STC)
- we can start/stop decoding and mute/unmute

Audio DSPs might have more capablilites for decoding and
post-processing:
- decoding more than one channel
- wave audio playback
- generating test tones
- mixing channels and 5.1 individual channel volume control
- bass/treble tone controls
- multi-channel (5.1) decoding or downmixing
- dynamic compression
- 5.1 front/rear channel delay

Additionally we have to control analog vs. digital audio outputs.

Some of these possibly can be mapped to simple GET/SET-paramter ioctls.

But you can also have a DSP firmware that offers independant functional
blocks which can be connected in a flexible manner. That would
complicate everything. I think ALSA has the capability to connect
audio device blocks and to have a flexible set of audio device
controls. But OTOH some of the audio features listed above are common
to many DVB SoCs, so it might be a good idea to have support for
them in the DVB API.

Please Let me know what your requirements are wrt audio.


Regards,
Johannes


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