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

Takashi Iwai tiwai at suse.de
Tue Aug 3 07:51:07 CEST 2010

At Mon, 2 Aug 2010 14:33:38 -0500,
pl bossart wrote:
> >> 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?

Yeah, good chance to really implement something.
We certainly need some solid channel for the extra information like


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