On site https://developer.apple.com/videos/play/wwdc2019/701/ the presentation video does not work. The error message "No video with supported format and MIME type found" is displayed. The video plays on Safari and Chrome.

I don't know if this is a browser or site issue, but when the error occurs, the transcript links are not accessible.

The src link [1] navigates to an M3U8 playlist file. A warning in the console says that:
HTTP “Content-Type” of “application/x-mpegurl” is not supported. Load of media resource https://devstreaming-cdn.apple.com/videos/wwdc/2019/701ngx868rfo8jlj/701/hls_vod_mvp.m3u8 failed.
Per Bug 1272142 I would expect that Content-Type of application/x-mpegurl is supported.

Bryce do you have an idea what is going on?

[1] https://devstreaming-cdn.apple.com/videos/wwdc/2019/701ngx868rfo8jlj/701/hls_vod_mvp.m3u8

This appears to be due to a script error. Bug 1559253 means that we show a warning that this is on line one, but actually it's much later. The error I currently see:

SyntaxError: invalid regexp group play.js:1:2

but in fact the issue is due to a named capturing group used later in the file at line 635. That line looks like this:

var testTime = /^(?<hours>\d+h)?(?<minutes>\d+m)?(?<seconds>\d+s)?/i,

and seems like our JS engine doesn't support named capturing groups, so this fails.

If I MITM myself and replace that script with one that changes the line to

var testTime = /^(\d+h)?(\d+m)?(\d+s)?/i

then playback works. Strictly speaking, more of the script needs to be modified to use positional captures, but I found changing just that line was enough to confirm.

This affects Windows also, and I imagine all desktop platforms.

I'm not 100% clear as to why this breaks our playback, but assume that the JS here is being used to convert the HLS video into a desktop compatible format, and if the script doesn't work then we try and play HLS and fail.

I'm going to leave this open for now while we investigate, but don't think this is a playback issue. I think this is a matter of us needing to handle named regex captures, or that script being changed -- the former of which we can control, the latter, maybe not so much.

Bug 1362154 tracks our support for named capture groups.

Clearing NI, assigning priority so this doesn't appear in triage.

Works since bug 1362154 landed.