[pulseaudio-discuss] Decode SPDIF compressed formats

Denis Shulyaka shulyaka at gmail.com
Wed Jul 12 22:33:29 UTC 2017

12 июля 2017 г. 23:58 пользователь "Tanu Kaskinen" <tanuk at iki.fi> написал:

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.

Ok, I will ask there. I've found datasheet for my hardware (CM106) and I
can see it that the information about whether the stream is compressed and
its sample rate is available to the driver. I just need to figure out if
ALSA gets it and propagates to PA.

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.

After some more googling I've found that there is IEC61937 standard that
defines which audio codec is used.

Thank you for your support, I'll now try to understand how ALSA works first.

Best regards,
Denis Shulyaka
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