Problem is still there. Has been here for a long time. I honestly wish there was paid version of Opera or bounty programs that would allow us to pay Opera devs so they could fix these huge bugs.
Windows 10 Edu (1803) 64-Bit
Opera 58.0.3135.127 (latest as of writing)
Audio cuts off 9 seconds in. The last 2 seconds can be heard after a second playback: https://twitter.com/xxGodsLastGift/status/1114036356576088064
Tried without ad-blocker
Tried in Opera Beta 60.0.3255.20 (no extensions) (latest as of writing)
Tried in Opera Developer 61.0.3275.0 (no extensions) (latest as of writing)
No flags touched
Tried an new user account, clean profile, same problem
Works in Chrome 73.0.3683.103, Firefox 66.0.2, and Edge 42.17134.1.0 (all latest as of writing)
On these browsers where it works, at 9 seconds the audio jumps in volume and also has a different sound to it as if it changed mics(?)
I tried replacing the files in Opera's WidevineCDM folder (C:\Users[username]\AppData\Roaming\Opera Software\Opera Stable\WidevineCDM\4.10.1196.0) with the files from Chrome's WidevineCDM folder (C:\Program Files (x86)\Google\Chrome\Application\73.0.3683.103\WidevineCdm). Even tried replacing the whole WidevineCDM folder with Chrome's.
Still same problem.
Opera is using WidevineCDM 4.10.1196.0 while Chrome is using WidevineCDM 4.10.1303.2
This is intermittent. Some videos work fine, others don't. The video in the Tweet that I linked above fails every time in Opera and works every time in every other browser.
Twitter (and Facebook?) is almost unusable in Opera with this problem.
There's another thread on this too: https://forums.opera.com/topic/30327/twitter-videos-sound-problem