Posting a link to a getyarn.io clip appears to onbox in the preview, but the actual post causes the browser to download a .mp4 file. More annoyingly, this happens any time the post comes into view, since I assume it’s being re-rendered.
It looks like the content type served by getyarn.io is application/mp4 instead of video/mp4, so that may be relevant.
Here’s an example URL, escaped for obvious reasons:
This bugs me too…I’ve always to know how to change a site’s MIME type…happens a lot with my web server (it’s something, no clue if Apache, nginx, JBossWeb, etc)
I just tried it on https://try.discourse.org and it worked fine? Is it possible they fixed the MIME type or is this a browser specific issue? I tested on the latest Chrome.