[mythtv] Digital audio passthrough

[James Courtier-Dutton]

On 15 September 2010 03:41, Jean-Yves Avenard <jyavenard at gmail.com> wrote:
> Hi
>
> On 15 September 2010 04:19, James Courtier-Dutton
> <james.dutton at gmail.com> wrote:
>>> When I try to open:
>>> front:AES0=0x6,AES1=0x82,AES2=0x0,AES3=0x2
>>>
>>
>> What is "front" doing there. Use "iec958" instead of "front".
>
> You've missed my point.
>
> With 0.24 I tried to remove the need for a dual setup of the audio device.
> So the user select one of the audio devices detected. We try to make a
> best guess to check if this device supports digital audio or not ; if
> we are sure it is a digital device or we don't know, the user has the
> ability to check the AC3 and DTS boxes for configuring passthrough.
>
> Before opening the audio device, we ran the equivalent of iecset on
> the card the device is attached to. This worked so far, including for
> people using ALSA:default. The only exception has been with Richard in
> that ticket. I haven't had any reports that it wasn't working for
> anyone else...
>
> So what I've changed now, is instead when opening the audio device for
> digital passthrough, I insert AES0=0x6,AES1=0x82,AES2=0x0,AES3=0x2 in
> the name.
>
> It's working if the user selected ALSA:iec958 or ALSA:hdmi ; but they
> are not the only two devices a user can select allowing digital
> passthrough as far as alsa is concerned (in particular I'm referring
> to the "default" which is returned during the enumeration of the audio
> devices)

I am only trying to help you from an ALSA developer point of view.
I highlighted the correct way of doing this, and you choose to do it
another way.
For example, your method will fail for a majority of the Creative
sound card range, but will work with most, but not all, cheap
motherboard based sound cards.

AC3 pass through requires a different setup of the audio device than
say 2.0 Stereo (2ch), and different from 5.1 surround(6ch).

I would recommend the following:
Have a setting for speaker arrangement, options as follows:
1) 2.0 Stereo   (plug:front)
2) 4.0 Surround (plug:surround40)
3) 5.1 Surround (plug:surround51)
4) AC3 Pass through. (iec958:etc)
Have another setting for card number:
1) Name of first card
2) Name of second card
3) etc.