[Intel-gfx] Problems with HDMI audio on Intel DG45FC motherboard

[David Härdeman]

On Wed, Oct 14, 2009 at 10:00:44AM +0800, Wu Fengguang wrote:
>On Wed, Oct 14, 2009 at 09:54:55AM +0800, Zhenyu Wang wrote:
>> On 2009.10.11 23:45:13 +0200, David Härdeman wrote:
>>> 
>>> a)
>>> 
>>> Channel mapping seems funky. I have a 5.1 speaker setup (though the 
>>> receiver supports 7.1) and using "speaker-test -c 6" or "speaker-test 
>>> -c8" with the hdmi output will generate output to the different speakers 
>>> but not the intended ones. Speakers are connected correctly though 
>>> (since the channels are correct if I use passthrough to send a raw AC3 
>>> stream through either the S/PDIF or HDMI connector). This only occurs 
>>> when using HDMI.
>
>This is known problem. The G45 HDMI codec does not support channel
>mapping, so the mapping must be handled in user space. Future Intel
>HDMI codecs may add support for this feature.

Two questions (and sorry if the questions show my lack of understanding 
of how this is supposed to work):

i) Can't the driver at least provide reasonable defaults? If playing a 
six channel audio, it seems reasonable that the user would like the 
tracks to play to the speakers conforming to a 5.1 setup?

ii) Is there any documentation somewhere on how this mapping is supposed 
to be performed in user space?

>>> b)
>>> 
>>> Each time a new audio starts playing, there seems to be a 50/50 chance 
>>> of complete silence, meaning that for each track change while listening 
>>> to music (for example), the entire track will either play or stay 
>>> silent.
>>> 
>>> This only happens when using HDMI, not S/PDIF. The problem occurs with 
>>> both MythTV's music player and when watching a movie with Xine.
>
>Complete silence for how much time?

For the entire duration of the particular movie/audio track/video 
clip/whatever.

So for instance, if I'm playing a list of tracks using MythTV, each 
particular track will either play completely *or* there will be complete 
silence for the duration of the track.

Same goes for showing a movie or a video clip with mplayer or 
xine...either the audio will work for the entire duration of the 
movie/clip or there will be complete silence for the duration of the 
clip.

This can be "fixed" by just stopping mplayer/xine/whatever and starting 
the program again with the same media until it works, but it's pretty 
annoying.

My uneducated guess is that there's some kind of content negotiation 
going on at the beginning of each new media playback. On the front of 
the receiver there is a LCD display which shows info on the current 
audio setup (number of speakers, type of audio, etc), and it flickers 
briefly at the start of each new track/video/etc before it shows the 
correct situation for the current media...perhaps there is some problem 
with this negotiation.

I got some feedback from another user on alsa-user (CC:ed):
http://article.gmane.org/gmane.linux.alsa.user/33393

And he had similar but not identical problems (2 second silence at the 
beginning of tracks, but not silence for the entire duration of a 
track), so perhaps different receivers react in different ways to 
something unexpected in the HDMI stream?

Regards,
David