[pulseaudio-discuss] Decode SPDIF compressed formats

Tanu Kaskinen tanuk at iki.fi
Wed Jul 12 20:58:14 UTC 2017

On Wed, 2017-07-12 at 22:29 +0300, Denis Shulyaka wrote:
> Well, that was more or less expected. Is such support planned?

I haven't heard of anyone planning to implement the feature.

> It means I need to write my own decoding application. But that leads me to
> another question:
> When I open the stream, how do I know its format? And how can I detect when
> it changes?

I don't know how the endpoints are supposed to agree on the format, and
what kind of interface alsa provides for that (if any). The alsa-devel
list might be more appropriate for questions about spdif details.

> I've came up with an idea to try different codecs and sample rates until I
> get something without decoder errors and not looking like a white noise,
> but well... you know... there must be a less ugly solution for that! (And I
> will have a really hard time detecting the format if my source _is_ a white
> noise for some reason).

I don't think it's necessary to figure out whether the data looks like
white noise. I believe compressed formats have some identification
bits, and if the data matches no compressed format, then I think it's
fine to assume that it's stereo 16-bit PCM data. Figuring out the
sample rate may require waiting for a bit to see at which rate the
sound card is producing audio. Maybe this is why at least some spdif
receivers lose a bit of audio from the beginning when starting to play
over spdif.



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