Maybe OP just xor'd the files with each other and the result was the RANDOM_STRING string followed by a pile of \0 bytes, repeat.
Edit: To clarify, I meant the encrypted and temporarily-decrypted-by-the-wrapper-script versions of the same .mov file.
Edit: To clarify, I meant the encrypted and temporarily-decrypted-by-the-wrapper-script versions of the same .mov file.