Media signing, unclear optionality of the hash list element

[ocampana-videotec]

In section 5.7.7 we have:

When this tag is present in the SEI payload the validation side can validate individual NAL Units. When this tag is not present in the SEI payload the validation side can only validate all NAL Units that has been signed, which in a normal case becomes all frames in a GoP.

What's the difference between the two sentences?

[ocampana-videotec]

Related to this there is Section 5.8 Low Bitrate Mode

As mentioned in the Limitation Section above, the SEI frames can become large due to the hash list. To lower the bitrate overhead, the device has the option to skip the Hash list tag; See above. The tradeoff is that it is no longer possible to identify individual invalid and/or missing frames.

So, first of all, section 5.7.7 should refer to 5.8 and/or section 5.8 should refer to 5.7.7

Second, we need to clarify what happens if we skip this element. In each General GOP information we have the hash of the I frame of the previous GOP. So we can validate the I frames of the stream.

I therefore deduct that the second sentence in section 5.7.7 really means

When this tag is not present in the SEI payload, the validation side can only validate the I frame in the GOP and identify missing GOPs.

But it this the correct understanding?

[bjornvolcker]

Thanks for spotting this. It is really poor wording and I will remove it from 5.7.7 and explain it better in Section 5.8 Low Bitrate Mode. Will also cross-reference the locations.

[sujithhanwha]

Closing this issue based on 4/18 VEWG telco discussion.