according to the SAMPLE-AES encryption method cited by the
HLS spec (informational RFC called draft-pantos-http-live-
streaming).

This encryption method is being incorporated in the Common
Encryption specification ISO/IEC 23001-7 3rd Edition as the
'cbcs' scheme.

Parsing of the stream requires it to be prefixed with extra
TS packets that carry encryption metadata. These packets
are formatted according to ISO/IEC 23001-9 "Common
encryption of MPEG-2 transport streams".

This CL is dependent on a prior CL (1490613005) that allows
conveyance of the extended encryption metadata through the
pipeline.

BUG=568326

Review-Url: https://codereview.chromium.org/1517473002
Cr-Commit-Position: refs/heads/master@{#436058}