AES-CTR mode full sample and video NAL subsample encryption.
AES-CBC mode partial video NAL pattern encryption. For video, the spec allows various encryption patterns.
The same as "cbcs" mode, but with a specific encrypt:skip pattern of 1:9 for video.
https://www.w3.org/TR/encrypted-media-2/#dom-mediakeysystemmediacapability-encryptionscheme