[mythtv-users] HDMI sound works for AC3 2-channel, but not 6-channel

[Steven Ihde]

On Apr 2, 2012, at 10:46 PM, Jean-Yves Avenard wrote:
> You should lodge a bug to the ALSA folks. That ALSA reports that your
> audio card supports 32 bits audio, when it doesn't...
> Do so on either their bug tracker
> (https://bugtrack.alsa-project.org/alsa-bug/login_page.php)
> or via their mailing list

Thanks again for your help.

My card has a CMI8768 chipset.  After digging around a little, it appears it's intended that it supports a 32-bit sample size, for the purpose of allowing 24-bit samples.  See for example this commit

http://git390.marist.edu/cgi-bin/gitweb.cgi?p=linux-2.6.git;a=commitdiff;h=57bd68b8b18608cf2729f97fcb984b8521d19551

I went ahead and reported the bug with Alsa to point out the 32-bit samples produce silence after reproducing this with speaker-test.

Perhaps others might be interested; I found it's possible to work around this issue without recompiling MythTV by using alsa-lib's plug plugin.  Adding an entry like such to /etc/asound.conf:

pcm.xyz {
	type plug
	slave {
		pcm "hw:1,2"
		format S16_LE
	}
}

Defines a new device "xyz" to convert input to S16_LE, and passes it on.  This seems to work as well.

-Steve

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