What about a system that saves in some way the hash in a Blockchain, and if you, eg, XOR the hash of the video with the hash of the previous block you will "certainly" know that the video was created between the previous block and the block where the hash is saved in. That's a starting point.

"Crack the hash"? Does this mean you were employing some novel hashing algorithm and relying on its secrecy? If so your employer were never serious about security in the first place. Hardware attestation is more or less a solved problem, and that solution does not involve secret algorithms.

Now sell them version 2.