In a recent update to Elementary OS the opera browser stopped playing videos on twitter.
Distributor ID: elementary
Description: elementary OS 0.4.1 Loki
The version with the problem is opera-stable_54.0.2952.41_amd64.deb
I downgraded my opera browser to opera-stable_53.0.2907.68_amd64.deb
This appears to have fixed the problem.
I was able to download the older version from here ~> opera-stable_53.0.2907.68_amd64.deb
Not sure is this affects other distributions of Ubuntu.