Steps to replicate the issue:
- Open https://en.wikipedia.org/w/index.php?title=L%27Arriv%C3%A9e_d%27un_train_en_gare_de_La_Ciotat&oldid=1220458415#Contemporary_reaction
- Click on either video thumbnail
What happens?:
Nothing except a flash of a dialog.
What should have happened instead?:
The video plays.
Other information:
Compare the files here.