Self hosting is of interest to avoid monthly fees / per event fees - I'd rather pay up front for software, run it myself and not have to pay hundreds / month - additionally, our (as most would) attendance would fluctuate - numerous times we paid for more seats at Webex only to have not as many attend as we anticipated, but the same conversely happens also - we paid for a low tier and more wanted to attend. Sometimes you don't know how many people will be interested in a specific topic, even though we try to gauge interest by forcing registration via our website.
Also - self hosting might lend itself to tighter integration. It would be awesome to embed the broadcast page directly into my events page, instead of emailing everyone a link to webex and maybe they got the email, maybe they didn't, maybe they missed it, etc...
.mp4 is fine - was just concerned it might be some proprietary format like Webex uses.