Eclipsa Audio 5.1 and 7.1 tracks get converted to a "2 channel" Dolby Digital Plus 5.1 stream

[branches78]

I uploaded this video to YouTube on feb 24th with Eclipsa Audio 5.1 but I didn't know about the following situation until I tested the video on a device without Eclipsa Audio support (Google TV Streamer).

Besides that the YouTube encoder has been converting previous uploads with Dolby Digital Plus 5.1 to Eclipsa Audio 5.1, YouTube has also been converting new video uploads with Eclipsa Audio 5.1 and 7.1 tracks to Dolby Digital Plus 5.1 but the surround channel information and the center channel information are being downmixed to the left and right channels. I was able to find out this with my AV receiver.

I then used a tool called "Parabolic" which is useful to download YouTube videos and found out that my video was encoded to Dolby Digital 5.1 and Dolby Digital Plus 5.1 streams so I downloaded the video and tested it directly on my receiver where I confirmed that the surround and center channel information were downmixed to the left and right channels.

These are the audio codecs available for download where the 328 is Dolby Digital Plus 5.1 and the 380 is Dolby Digital 5.1:

And this is what mediainfo shows about the codec:

It's worth mentioning that Parabolic doesn't show the Eclipsa Audio tracks, they remain hidden, I imagine Google has restricted access to them.

It also worth mentioning that the video I uploaded has 6 channels of audio but the real mix is 4 channels where the center channel information and the LFE channel information are absent, however, it is encoded as 5.1 because that's how the original track is, though my other videos with a full 7.1 channel mix are also affected by the situation.

The TV where I play Eclipsa Audio videos on YouTube is an LG QNED 55QNED85A that received a firmware update on January with Eclipsa Audio support but it seems to be buggy because the left surround and right surround channels don't output sound with Eclipsa Audio 5.1 channels and I don't know if this issue lies on the TV or on the Eclipsa Audio implementation on YouTube.

[cjee21]

It's worth mentioning that Parabolic doesn't show the Eclipsa Audio tracks, they remain hidden, I imagine Google has restricted access to them.

Google does not restrict access to them. The IAMF stream is ID 773 and is IAMF using Opus and encapsulated in MP4. You do not see it because the app you used is not updated to support it.

[branches78]

Thank you for clarification, I though they were hidden on purpose.

[cjee21]

Maybe YouTube did change something. I just tried and even an app that can retrieve the IAMF stream previously now fails to detect any IAMF streams as well.

[branches78]

In the case of Parabolic, I've never seen the IAMF tracks on that app, hence why I though they were hidden on purpose.

[branches78]

I just tried and even an app that can retrieve the IAMF stream previously now fails to detect any IAMF streams as well.

Can you please tell me what is the app you use?

[cjee21]

Can you please tell me what is the app you use?

https://github.com/yt-dlp/yt-dlp/issues/12349

IAMF appeared and can be downloaded previously although the app does not explicitly support it yet. However it no longer detects it now. Even E-AC3/AC3 now disappeared and requires extra actions to make them reappear but I have not been able to make IAMF reappear. Maybe it's due to YouTube limiting IAMF to only certain supported TV apps and they added more protection to streams for TV apps but I'm just guessing. So it makes it difficult to check how YouTube is encoding the streams now.

[cjee21]

Here is how the IAMF track for https://www.youtube.com/watch?v=ItvQeAkpG-M looks like back when it was obtainable if you are interested.

Generated with

MediaInfo.exe "Introduction to Eclipsa Audio (IAMF).m4a" >> MediaInfo+trace.txt && MediaInfo.exe --trace_level=1 "Introduction to Eclipsa Audio (IAMF).m4a" >> MediaInfo+trace.txt

MediaInfo+trace.txt

[branches78]

Hello @jwcullen can you please clarify why you moved this ticket to the discussions section since this is clearly a bug on YouTube right now?

[jwcullen]

We recently opened up the Discussions section. As part of that, I reorganized issues with the aim of keeping them focused directly on iamf-tools.

We envision the Discussions section as a better place to discuss any other platforms, software, firmware, hardware, related to IAMF or Eclipsa. Here the community can help share their workflows, ask questions, discuss tips, or bugs when trying to create or playback the format.

For this specific thread, one of my colleagues looked into the issue. It's true YouTube sometimes serves a "2 channel" 5.1 stream. The issue is being tracked. Currently this is no workaround.

[branches78]

Hello, @jwcullen, thank you for clarification.

As an additional clarification, YouTube has always been doing the "2 channel" 5.1 stream bug and not sometimes, the latest video where I see the issue is this one uploaded on march 10th 2026, previous uploaded videos with 5.1 channels haven't been affected.