I don't understand, do you have access to a CDN or you're saying that soundcloud and ch9 have a CDN?
The problem is one of storage, as I don't think all the videos here on channel 9 are saved in SQL.
I don't think they're stored in a database at all. If I were to create such an architecture, I would use a RDBMS for storing metadata and just a file system to store the actual large files.
NoSQL seems to be the option, but I need load balancing and multitenancy, the ability to process volume shadow copy and so on and pretty good reliability and performance
My understanding of NoSQL systems is that they're used mainly where you have to process massive (upwards of millions of items) amounts of loosely typed data, not where you have a small amount of large files...