(backblaze ceo here) B2 is a great origin store for your video files. If you're streaming to lots of viewers, using a CDN with Backblaze B2 is optimal. We partnered with Cloudflare as a founding member of the Bandwidth Alliance so you can store your videos with B2 and transit them for free to Cloudflare, which can serve to your viewers.
Please correct me if I'm wrong, but my understanding was that Cloudflare should not be used to deliver video files unless using Cloudflare's "stream" product, IE specifically this [1].