HTML5 video playback (YouTube and other streaming sites) keeps breaking in Tahoe. Not lagging… I mean *completely* broken!

[markpaterson]

I have a Mac Studio M2 Ultra with Tahoe 26.0.1.

Everything in Tahoe was fine for a few days until suddenly any site with HTML5 video would fail to play back video. (ie YouTube and basically any streaming site). When you click play it would just spin forever and then YouTube would throw up an alert saying "If playback doesn't begin shortly, try restarting your device". I restarted, and it doesn't fix it.

Other things I've tried, to no success…
(1) Cleared Safari cache
(2) Tried Chrome instead of Safari
(3) Rebooted modem and router
(4) Tried WiFi instead of Ethernet
(5) Created an new user account

The only thing that fixed it was booting into Recovery mode and reinstalling macOS Tahoe over top of my existing installation. Nothing is wiped during this process, but every system component is replaced. It's like a deep OS level component got corrupted at some point?

I thought that was the end of it, until today it started happening again!

YouTube works fine on my other updated devices (M2 MacBook Air with 26.0.1, iPad Pro with 26.0.1) but I don't use those as much so I don't have a true comparison.

This is incredibly frustrating. I can't be reinstalling Tahoe every couple of days. What a sh*t show!

UPDATE - I can completely rule out a network issue! I just tried running my own portfolio website locally in Safari and Chrome and the HMTL5 video does not playback! These mp4 files play back just fine in Finder.

 

[snakes-]

Can be because of add-ons or adblockers. I solved this with refresh button and wait some seconds or try it to play in a new tab.

 

[markpaterson]

Can be because of add-ons or adblockers. I solved this with refresh button and wait some seconds or try it to play in a new tab.

Happy that worked for you but that's not the solve here.

As I said, it even affects local websites. My extremely basic hand coded portfolio site doesn't care if you use an ad blocker or not, yet it fails to play back HTML5 video in Tahoe, even when running locally.

Yes, I have Stop The Madness Pro installed, but I still had that installed after reinstalling Tahoe (which fixed the issue first time around). For what it's worth, I just disabled the extension, and it didn't make any difference.

 

[markpaterson]

Ok, I once again just re-installed Tahoe over top of the existing system and lo and behold, HTML5 video is working again. Like I said previously, this appears to be the only fix!

 

[markpaterson]

I’ve set up an hourly monitoring script that computes MD5 checksums of all video frameworks and caches, and logs any changes along with GPU/video decoding services and all LaunchAgents/Daemons, creating a new timestamped log each run. It also sends a macOS notification if anything changes. This way, I can capture exactly which file or process causes the HTML5 video playback to break when the issue reoccurs.

All is fine right now, but as soon as it stops working again hopefully I will have a better idea what is causing the issue.

 

[Starfia]

This feels like something I've occasionally encountered (but, like Snakes, apparently hadn't found insoluble). Please feel free to reply and update if you get to bottom of it – I'd be curious.