I know next to nothing about widevine decryption so forgive my ignorance - I was wondering if I download protected files now and get a widevine key later from another device, would I be able to decrypt the file with that key? or must the decryption be done with the same key/device that was used to download the file?
Ah, I had the numbers backwards. Is L1 heavily in-use?
Yes. Depends on the platform. For example with Netflix L1 is required for full HD, L3 will only give you access to SD content.