[mythtv-users] additional configuration items for new sound system in 0.24

[Brian J. Murrell]

On Wed, 2010-11-17 at 10:14 +1100, Jean-Yves Avenard wrote:
> Hi

Hi,

> if you want AC3 to be decoded by myth, uncheck AC3 passthrough.

Generally, I do, and if an optical connection could carry 5.1 LPCM
that's exactly what I would do, but it doesn't, hence my need for a
compromise.

> I won't be adding such option. The idea is to simplify the setup, not make
> it once again overcrowded with options 99% of the people won't use

That's fair enough.  There is an "Advanced" section in Audio setup which
is normally not visible and not crowding the main UI of common options
that I think is a perfectly fair place for this kind of extra
configuration.

> This is already done internally.
> Myth knows how many pcm channels the audio card support.

But it doesn't know how many pcm channels are available end-to-end.

Yes, my audio card might be able to support 5.1 pcm channels (to the TV
on HDMI) but only 2 of those will make it beyond the TV to the receiver
(on an optical connection).  That's something that Myth will never be
able to figure out on it's own and needs the user to tell it.

> so if using spdif, it will send PCM for stereo only, anything multichannels
> will be sent as DTS or AC3.

I think maybe you are missing the whole picture:

MythFE-->--HDMI-->TV-->toslink-->receiver.

Indeed, as you say, Myth can determine the capabilities from itself to
the TV but it cannot determine the capabilities from the TV to the
receiver.

Ultimately my goal is to prefer to have Myth decode the audio when it
can (i.e. 2ch DD) but also recognize when it can't (5.1ch DD/DTS) and
pass it through otherwise and because the receiver is not directly
connected to Myth, Myth needs help to understand what it can and can't
do.

ITSM that if the assumption is that when LPCM, DD and DTS are all
selected, that LPCM is preferred when possible, all that's needed to
achieve my goal is a single additional option to tell myth how many PCM
channels are available, end-to-end.  With that in the "Advanced" area,
it doesn't seem to me to be terribly onerous on the UI/configuration.

The use-case that backs all of this up is that as I mentioned before, my
receiver exhibits a second or two of latency when it's given DD to
decode.  That means that when you start playing (say) a television
recording you have to back up to get the second or two of audio that was
playing while the receiver "kicks into" DD decoding.  The same thing
happens on every commercial skip or pause -- you have to wind back a few
secs to get all of the audio.  This is most common (and annoying) with
the 2ch AC3 that one typically gets on digital cable.

For 5.1 content, for me at least (without HD cable), this typically is
only movies, where there are no commercials to have to skip and thus the
number of times one has to deal with the receiver's DD latency is low
enough to be acceptable.

And all of this can be resolved with only one additional configuration
knob.

Thots?

b.

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