[goestoo]

Their terms say https://www.cloudflare.com/service-specific-terms-applicatio...

  Unless you are an Enterprise customer, Cloudflare offers specific Paid Services (e.g., the Developer Platform, Images, and Stream) that you must use in order to serve video and other large files via the CDN

https://www.cloudflare.com/service-specific-terms-developer-...

  The Cloudflare Developer Platform consists of the following Services: (i) Cloudflare Workers, a Service that permits developers to deploy and run encapsulated versions of their proprietary software source code (each a “Workers Script”) on Cloudflare’s edge servers; (ii) Cloudflare Pages, a JAMstack platform for frontend developers to collaborate and deploy websites; (iii) Cloudflare Queues, a managed message queuing service; (iv) Workers KV, D1, Durable Objects, Vectorize, Hyperdrive, and R2, storage offerings used to serve HTML and non-HTML content; and (v) Workers AI, a Service that allows customers to use Cloudflare’s inference infrastructure to invoke select third-party machine learning models (subject to applicable open source licenses or third-party terms of use for such models).

Based on their terms, serving video in R2 should be fine.