HDMI Audio Bridge

[zeerround]

Here is the first public release of HDMI Audio Bridge, for Windows 10 and 11. This is version 1.4.

The name is due to its function of live encoding audio with Dolby Atmos, such that you can pass 12 channels (7.1.4) of audio from your computer to an HDMI connected AVR or Soundbar, etc. Without this, despite the current HDMI standard for 32 channels of LPCM audio, consumers are limited to 8 channels of unencoded audio over HDMI.

The purpose is to help in building out the ecosystem for hobbyist immersive up-remix. As it is, most hobbyists don't have or can't afford sound devices with more than 8 channels, and most AVRs don't have more than 8 analog inputs in any case. So one aspect of HDMI Audio Bridge is to let up-remixers live monitor their mix, via HDMI to their AVR.

To do this, you also need a reliable 12 channel virtual audio cable, to connect your DAW or other audio program to HDMI Audio Bridge. One that works very well (and I have tried them all) is LoopBe Audio, and there is a free trial and purchase is only ~$20 US. https://www.nerds.de/en/loopbeaudio.html

The 2nd part of the ecosystem this is intended for is the playback of hobbyist immersive sound up-remixes. Because most Hobbyists can't afford (and Dolby wont sell to, in any case) Atmos encoders, DTS X encoders, or Auro 3D encoders. We need a "free" encoder for immersive formats (as .wav or even .wv 12 channel files are HUGE). One such free format, and part of IAMF/Eclipsa Audio is opus. Opus can be freely used to encode 7.1.4 and other immersive formats with ffmpeg. As we don't (yet) have AVRs that can decode opus/IAMF/Eclipsa audio, HDMI AUDIO Bridge can decode and play back opus, sending it on to your AVR as Dolby Atmos 7.1.4.

This version of HDMI Audio Bridge can playback 12 channel 7.1.4 files in .wav, .wv, .opus, opus.ogg, and opus.mp4 format. Up-remixers working in other immersive speaker layouts will need either down mix 9.1.6 or 9.1.4, to 7.1.4, or route their fewer channels into the 7.1.4 channel order, skipping unused channels. Of course for Dolby Atmos, if your system has fewer than 7.1.4 speakers, Atmos will downmix to your speaker layout.

I will be following up with drag and drop scripts to encode via opus, and even iamf/eclipsa. Iamf/Eclipsa decoding and playback (7.1.4) will be included in the next version of HDMI AudIo Bridge.

Like my other audio tools, SpecScript, SpecWeb, etc. This is my gift to the community, but if you want to encourage me to keep developing audio tools or support me in my efforts there is a donation link included in the documentation.

Here is the link to download: h**ps://surroundbyus.com/sbu/download/HDMI_Audio_Bridge_v1.4_1.4.0.0_Test.zip

Just copy and paste the link into your browser and replace the ** with tt

The Dolby Access App, if you don't already have it, is needed to enable Dolby Atmos support on Windows. The "Dolby Atmos for home theater" part of the app is free. They only charge for "Dolby headphone", which is not used in this case.

 

[SeeMoreDigital]

One such free format, and part of IAMF/Eclipsa Audio is opus. Opus can be freely used to encode 7.1.4 and other immersive formats with ffmpeg. As we don't (yet) have AVRs that can decode opus/IAMF/Eclipsa audio, HDMI AUDIO Bridge can decode and play back opus, sending it on to your AVR as Dolby Atmos 7.1.4.

Oh wow, I didn't know this about Opus. (But I do know that AAC-LC offers up-to 48 channels with sampling frequencies between 8 kHz and 96 kHz).

 

[zeerround]

I don't want to get too far of this topic of HDMI Audio Bridge, but my understanding of AAC multichannel is it's one of those codecs where once you go beyond 8 channels you really need a commercial/differently licensed codec/library, that can't be distributed with ffmpeg binaries (You have to build it yourself and not share).

AI says: "you might want to consider using alternative AAC encoders like libfdk_aac for better multichannel support, as the native FFmpeg AAC encoder might not provide optimal quality for such complex channel layouts."
and
"Opus would generally provide better quality for 12-channel audio. The Opus codec was specifically designed with modern multichannel formats in mind and has excellent support for high channel counts."

That said, AAC is one of codecs supported in IAMF ("IAMD is codec agnostic") , but so far the encoding examples we have, using "free" versions of ffmpeg, use opus. See https://github.com/AOMediaCodec/iam...tools.md#encode-wav-files-to-iamf-with-ffmpeg

HDMI Audio Bridge currently supports 12 channel straight opus, and I have a version here that also supports 7.1.4 iamf in .mp4, as encoded according to the above reference URL. My intention, however, is to have full support for any iamf .mp4 ecodings, decoded to 7.1.4 (to feed to AVRs and 7.1.4 Dolby Atmos).

 

[SeeMoreDigital]

This sounds really exciting...

 

[zeerround]

today I discovered how to get foobar2000 to play 12 channel opus files: https://www.quadraphonicquad.com/forums/threads/todays-foobar2000-learnings-7-1-4.37197/

So you can keep your beloved foobar2000 player, connect it's output to HDMI AUDIO BRIDGE with the LoopBe Audio cable and you're good to go for playback of 7.1.4 opus encoded up-remixes (The point being that the opus encoder in ffmpeg is both "high Quality" and free.