As reported in https://github.com/webcompat/web-bugs/issues/64104

STR:

1. Visit https://www.twitch.tv/videos/845353044 in Firefox Nightly 86.0a1 on desktop and observe the video player

Expected:
Video plays

Actual:
Not possible to play the video and an error is displayed:
"Your browser encountered an error while decoding the video. (Error #3000)"

From mozregression:

14:16.26 INFO: Narrowed integration regression window from [2a46f29c, 8dbba1ce] (3 builds) to [2a46f29c, 4c3e6fb9] (2 builds) (~1 steps left)
14:16.26 INFO: No more integration revisions, bisection finished.
14:16.26 INFO: Last good revision: 2a46f29c8cdd6f6269483e86c6e21e649ffa7127
14:16.26 INFO: First bad revision: 4c3e6fb95aa6184651f215d466e702ff7d1660d3
14:16.26 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=2a46f29c8cdd6f6269483e86c6e21e649ffa7127&tochange=4c3e6fb95aa6184651f215d466e702ff7d1660d3

I get the following in the console:
Cannot play media. No decoders for requested formats: video/mp4; codecs="avc1.42E01E mp4a.40.2", video/mp4;codecs="vp09.00.10.08", video/mp4;codecs="vp09.00.10.08"

Hi Jean-Yves, would you be able to take a look at this?

The error about being unable to play a media is bug 1674315

[Tracking Requested - why for this release]:

I can reproduce on mac too.

This bug will show up in 85 as we've enabled the RDD for the main decoders there.

regression on a major video site

[removed]

The regression range is invalid.

We've never been able to play this video (just tried with FF ESR68, 68, release and beta) ; the WMF AAC decoder gives an error when attempting to create 7 channels decoder.

Old Edge non-chromium based and IE 11 that are using the same decoder fail in the same fashion.

Nothing we can do about it until we can ship our own AAC decoder

Thanks for looking into this. The video actually plays in Firefox release (84.0.1) on my Mac. I run mozregression again and it still points to 1595994.

As for Windows - not working in release, and looks like never did.
Did you try playing it on Mac or Windows?

(In reply to Ksenia Berezina [:ksenia] from comment #6)

Created attachment 9194554 [details]
Screen Shot 2020-12-23 at 10.46.59 AM.png

Thanks for looking into this. The video actually plays in Firefox release (84.0.1) on my Mac. I run mozregression again and it still points to 1595994.

As for Windows - not working in release, and looks like never did.
Did you try playing it on Mac or Windows?

it works on my mac here.
This is a windows issue.

Are you saying it regressed on your mac?

Yeah, that's correct, it regressed on my Mac.

So basically on Windows it never worked (that's the original webcompat issue). And on Mac it's working on release, but not in Nightly.