Hash SEI without emulation prevention bytes

[bjornvolcker]

Describe the feature

Today, all NAL Units are treated the same, that is hashed after emulation prevention bytes are injected. It is rare not to use emulation prevention bytes, but some encoders can generate SEI frames given the payload, for which emulation prevention bytes are added by the encoder. In such cases, it is more efficient to hash without them to avoid unnecessary memcpy.

Added value

Use a bit in the reserved byte to signal if the SEI should be hashed with or without emulation prevention bytes.