Declare intent to use sample-aes later in the stream.

Allows the declaration in an unencrypted part of a stream of an intent
to use sample-aes encryption later. This allows the decoding backend to
be properly initialized with the appropriate encryption scheme.
This involves prefixing a subset of the encryption metadata that is used
to indicate encryption, but omits the key id and IV.

This will typically be used in a live stream, when tuning in during
an unencrypted part, e.g. a commercial.


Cr-Commit-Position: refs/heads/master@{#505415}
11 files changed