[pulseaudio-discuss] HDMI support

[Lennart Poettering]

On Wed, 01.04.09 18:42, pl bossart (bossart.nospam at gmail.com) wrote:

> If I use HDMI to connect to a receiver, the number of supported channels
> depends on the number of speakers and the capabilities of the receiver. The
> HDMI protocol provides a means for the receiver to let the transmitter know
> its speaker configuration, but so far you cannot query it from ALSA, there's
> just no interface for this. Your best bet is to try to open the device with
> an increasing number of channels and see when it stops working.
> 
> When I look at the PulseAudio code in alsa-utils.c , it looks like the HDMI
> profile is set to two channels, if more channels are requested the device
> selected will be the first surroundxx profile that is a superset of the
> channel map.
> Now I have the following questions:
> - First is my understanding correct?

Yes.

> - Does this solution entail any configuration of  /etc/asound.conf to link
> surroundxx with the HDMI device number? And if this is the case, how
> compatible is this with hot-plug (depending on the order in which I plug all
> the audio devices the number could be different).

Nah. It's just a matter of defining more profiles. I have no HDMI and
I have no clue about the channel orders, except for the obvious case:
2ch. That's why there is currently only one profile known
"hdmi-stereo". So what's missing is duplicating the current hdmi
profile for more channel mappings and that's about it.

> - last, if the number of speakers on the receiver side is smaller than the
> number of channels requested, who does the required downmix?

PA will configure what ALSA allows. Profiles are only tested with the
configured channel number. So if "hdmi-stereo" is being configured but
the HDMI device cannot do 2ch the profile will not be listed as
available.

If a client stream is then connected to the sink and the channel
mapping does not match, PA will do up/downmixing as necessary. It's a
pretty simple up-/downmixing however.

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
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