[mythtv-users] HDMI ac3 passthough audio

Allen Edwards allen.p.edwards at gmail.com
Thu Feb 12 18:00:32 UTC 2009

On Thu, Feb 12, 2009 at 9:38 AM, Steven Adeff <adeffs.mythtv at gmail.com> wrote:

> 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.
> --
> Steve

The way I read this and the documentation along with my understanding
of spdif is that plughw should not be able to do anything with a spdif
stream so plughw and hw should be equivalent for hdmi or spdif
streams.  I don't think ALSA can decode a spdif stream so it could not
do any rate conversions on it.  I put hw in the wiki so bypass
whatever extra code plughw would have in it.  I just want to make sure
I am saying the right thing and as hw works for me, I have no direct
reason to change the wiki to plughw.

Unless someone can say that hw doesn't work where plughw does work, I
will leave hw in the wiki.


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