Filler data NAL unit and SEI missing

[ksuehring]

From the N meeting notes:

- Adopt a starting point for HRD design as captured above, from an editorial combination of JVET-N0423 and JVET-N0350, using the most recent version of HEVC as the basis.
[..]
  - Filler data NUT and SEI
[..]

It seems, both have not made it into the specification text yet (although referenced in the HRD section)

[yk]

Good catch! I also noticed earlier that filler NAL unit is missing and referenced in Annex C. But on the other hand, I could not find a reference to filler SEI message in Annex C. My understanding is that filler NAL units and filler SEI messages are for encoders to make the bitstream constant bit rate when needed. But for that purpose, just having filler NAL unit is sufficient, right? Does anyone know the usefulness of filler SEI message once there is filler NAL unit?

[ksuehring]

Filler data NUT uses to be a VCL NAL unit, while the SEI is non-VCL. You need both types to exactly match the bitrate for the two HRD operation modes.

[yk]

Hmm, but in both AVC and HEVC filler data NAL units are specified as non-VCL NAL units...
And in Annex C (of both AVC and HEVC), filler data NAL units can be part of the bitstream for both Type I and Type II HRD conformance point...

[ksuehring]

You are right. They are non-VCL, but still in type l. But SEIs are only in type II, so they can be used yo adjust type II rate without affecting type I.

[yk]

Hmm, you are right. Then let's add both filler data NAL unit and filler SEI message. Since both were agreed at JVET-N, let's just add both into the editorial input document we are preparing for the upcoming JVET-P meeting.