A way would be to scramble or remove the file header after saving it somewhere else
Which means to recognize the format you will have to put back the header
But a motivated capable hacker would be able to recreate a working header
The military grade unbreakable way to encrypt a file is to use the one-time pad encryption (which is basically a XOR on the entire file)
Unbreakable because without the key you have 256 possibilities per byte
Any big file without a recognizable header would be showing off some red flags
So maybe you can put an ogg or MKV header (or other format) to an one-time pad encrypted file