I too gave that a thought and tried to do some calculations.

If I use the raw data in the buffer, it'll be around 1mb/f so 60mb/s in 800x420 24bit.

But, I intend to compress it somehow, although I never thought about video encoding.
I don't want to convert the raw data of the backbuffer, because this will slow the process, I want to just compress it and send it to be decompressed in raw data and then the raspberry will have to use it as is (device independent...)
That way, the raspberry will only need to decompress, not also convert or resize or anything...

I was thinking something like jpeg and then using the WEBP format, or directly using the WEBP (I didn't see any working examples, but Google did explain how the process works, so I thought I could replicate it in the future, after I get a few frames going.)

I'm not sure if the raspberry could handle any kind of decompression if its 60fps, but I'll experiment if it fails.

I'll give a look at h.264 later today I always download that kind of movies, but never thought about using this hah, irony.