[alsa-devel] How to handle HBR pass-through? (new PCM_FORMAT?)

pl bossart bossart.nospam at gmail.com
Mon Aug 2 21:33:38 CEST 2010

>> Looked at gstreamer, it seems to only have ac3-in-iec61937 support currently.
>> However, I'd guess gstreamer would additionally need some ways to 1) detect if
>> HBR is supported, and 2) detect if the connected receiver supports the
>> specific codec..
> Reusing the existing IEC958 status bits is OK for practical POV,
> indeed.  This makes also compatible with the existing user-space stuff.
> But I feel a bit uncertain when looking forward for future
> development.  More discussions needed.

The automatic detection is not possible for now no matter if you rely
on gstreamer or ffmpeg or something else.
The one thing that is missing for HDMI is to make use of EDID
information to report to userspace the capabilities of the receiver so
that apps or the audio policy make educated decisions on whether to
decode locally or use pass-through modes using iec61937. The HDMI spec
only mandates stereo/48kHz, and if you have an older receiver (2 years
old...) you may not have TruHD supported there. To the best of my
knowledge, there aren't any standard controls to report what the
receiver supports. I had some discussions with Takashi on this in the
past, looks like it's time to make this happen?

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