CENCv3 recommends only encrypting video data in slice NALs. Slice
data partition NALs should not be encrypted.
In the code, differentiate is_vcl and is_video_slice. They are the
same for H265; for H264, vcl NALs include slice data partition NALs
but video_slice NALs do not.
Change-Id: I91f4bdd76d25f0eac50e39aed350ebce3f667121
In H264, there may be multiple consecutive video slice NAL units
in the same frame. The original code assigns a new access unit
for every video slice NAL unit, which is incorrect.
Fixes#134.
Change-Id: I4d44271df48cb08867ddd02f7494fb3573af3356