[mythtv-users] HDMI ac3 passthough audio

[Joel Means]

On Thu, Feb 12, 2009 at 10:38 AM, Steven Adeff <adeffs.mythtv at gmail.com> wrote:
>
>
> pre-ALSA 1.0.19, HDMI was "supported" but indirectly, requiring
> asound.conf hacking. 1.0.19 explicitly supports HDMI, as you see, by
> listing it as a default device.
>
> when you do an aplay -L what you get listed is what devices ALSA
> creates for your sound card as a default.
>
> the asound.conf file lets you 'override' those with your own devices.
>
> plughw is a conversion layer for hw, depending on how you use it, can
> allow conversions for rate, channels, etc. From what I understand,
> used alone, will only perform rate conversion for PCM output but allow
> for bitstream'ed content to pass to the hardware untouched.
>
> hw is the direct channel to the device, unfettered by all the
> conversion layers that ALSA can perform. as such its very powerful,
> but requires specific intent and knowledge about your hardware and
> what your trying to accomplish.
>
> This is what I learned at least, and why I went with setting MythTV to
> use plughw as it would allow for the required rate conversions when
> playing back stereo audio as PCM but then also pass AC3/DTS untouched
> when used for that (ie -ac hwac3,hwdts in mplayer).
>
> Anyway, this is what I was able to gather when getting HDMI audio
> working on my mom's computer, for which I was successful, so at least
> some of it must be *true enough* to have gotten it to work =P
>
> --
> Steve
> http://www.mythtv.org/wiki/index.php/User:Steveadeff
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Good info.  Interestingly, even when hdmi wasn't listed in 'aplay -L'
output, I could still use it as a device to send audio through HDMI.
I got to looking at the files in /usr/share/alsa/cards (specifically
HDA-Intel.conf) and found that the hdmi device was listed in there.  I
am not sure why 'aplay -L' didn't show it.  In the same way, using an
older version of ALSA, 'aplay -L' didn't show the iec958 device, but I
could always use it.

Joel