[pulseaudio-discuss] review+pull-request: Passthrough support
bossart.nospam at gmail.com
Thu Apr 21 17:33:43 PDT 2011
> Yes. The C bits are usually ignored by the receiver since a lot of
> sources don't configure them well. But it turns out that in this case
> setting the non-audio bit is a mandatory setting.
I tried to implement this audio/non-audio switch by playing with ALSA
controls, however there are a couple of problems:
- the non-audio mode can only be set when the device is closed. There
are some protections in alsa-lib, meaning we would need to set this
mode on resume and go back to audio mode on suspend.
- it took me a while to realize that everything I programmed using
alsa controls (snd_ctl*) or configured with iecset on a command line
was just overwritten with default values when playback starts. the
alsa-lib hdmi/iec958 plugin resets all the values that you carefully
programmed with snd_ctl* calls, you really have to pass an argument to
this device when it is opened. Boils down to adding ",AES0=0x06" to
the device name in passthrough mode.
>> Is the ALSA device correctly being configured to 192 kHz?
> I will have to recheck for these two cases. I guess it is since I can
> see the D+ logo, but let me confirm for these two cases.
The frequency is correctly set:
rate: 192000 (192000/1)
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