Passthrough surround sound audio formats over HDMI

[CascadianGit]

Your system information

• Steam client version: 1676336721
• SteamOS version: 3.4.4
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

There's no way to output compressed surround sound audio over HDMI when docked, it only allows multichannel PCM.

I would like to use Plex on my deck and output DTS or Dolby Digital audio to my receiver, connected over HDMI.

This only requires passthrough over HDMI, no encoding.

Steps for reproducing this issue:

1. Install Plex through the Discover software center
2. Enable 5.1 audio in the audio control panel in desktop mode
3. In either desktop mode or gaming mode run Plex
4. Go to the audio settings in plex
5. Select the correct HDMI output
6. Select passthrough for the various surround sound audio formats
7. Play a video file with surround sound audio
8. Plex freezes and does not play audio
9. It works to play multichannel PCM if the surround sound audio formats are deselected for passthrough

[dborel]

This is broader than just passing media compressed audio out, although that would be a simple first step. Consoles offer Dolby Digital Live and real-time Pro Logic 2 encoding to deal with SP/DIF's data limitations for games.

[dborel]

Even the ability to send multichannel PCM to a separate HDMI or DisplayPort output would potentially unblock my use case: HDR TV and pre-HDR amplifier.