Dump everything you know about HDMI eARC here

[stigger]

So, I got a rewritable dummy HDMI plug, but to my surprise it did not affect the behavior. I started experimenting further and here is what I've found out:

- Neither the presence of the plug nor the difference in EDID configuration seem to affect anything, at least for PCM audio. For example, I tried to allow only 5.1 PCM in EDID, but the extractor would still switch to 7.1. This is a bit unexpected, because the MCU definitely reads out the sink EDID from the IT66121 chip. Not sure what it does with it.
- It looks like my TV (Sony A95L) always downmixes audio to 2.0 when configured to output PCM. The only time I saw a multichannel PCM output was when I configured TV to passthrough audio, and the media player to output PCM to the TV
- One of my goals was to output multichannel audio from the TV apps. So far it looks like the only way to achieve that (at least with my specific TV) is to passthrough the audio all the way to RPi and try to decode it there, if that's even possible.

 

[stigger]

Received the RPi 5 and tried actually recording the I2S input coming from the extractor. No surprises here: was able to capture PCM just fine. The passthrough streams are there as well, so far I only tried capturing with arecord, but the resulting data looks sane, restoring the original stream and decoding it seems doable.