My understanding is that when using the xor cipher, even if the key is truely random, the file could still be trivially completely decrypted for a repeating key

My understanding is that when using the xor cipher, even if the key is truely random, the file could still be trivially completely decrypted for a repeating key. It seems like a rather unwieldy cipher if you need to download a key which is nearly the same size as the video file.