[mythtv-users] HDMI ac3 passthough audio

[Allen Edwards]

On Thu, Feb 12, 2009 at 10:06 AM, Steven Adeff <adeffs.mythtv at gmail.com>wrote:

> On Thu, Feb 12, 2009 at 12:45 PM, Joel Means <means.joel at gmail.com> wrote:
> > 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
> >>
> >
> > 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
>
> right, the hardware is/was still supported, it just wasn't set up with
> a device name, so you could use the asound.conf to give it a device
> name, or use plughw/hw to tell your application to talk to it
> directly.
>
> as to whether the older ALSA versions fully supported HDMI for audio I
> don't know, but 1.0.19 supposedly can (bugs not withstanding =P )
>
>
> --
> Steve
>


I have been doing some fooling around tonight that might help here.  Not
sure of the exact syntax for specifying your
iec958=1 or hdmi device but let's assume that is it from the work you did
with aplay.

Try these as the default device in asound.conf:

  pcm.!default {
     type plug
     slave.pcm "iec958=1"
  }

or

 pcm.!default {
     type plug
     slave.pcm "hdmi"
  }


Let me know which one works please, assuming one does.


Allen
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