Opened 8 years ago

Closed 6 years ago

#1448 closed enhancement (wontfix)

offset_len_minus1 range

Reported by: kolya Owned by:
Priority: minor Milestone:
Component: Text Version:
Keywords: offset_len_minus1 Cc: bbross, wjhan, jct-vc@…


The spec says that valid range for offset_len_minus1 is [0, 31]. At the same time, offset_len_minus1=0 means that there is a slice segment of 1 byte size (entry_point_offset_minus1 == 0). But this is not possible coz every slice segment should contain at least 9 bits according to the clause

Thus the valid range for offset_len_minus1 should be described as [1, 31] and valid range for entry_point_offset_minus1 is [1, 232 - 1].

(on behalf of pavel.evsikov@…)

Change History (3)

comment:1 follow-up: Changed 8 years ago by kiranmisra

Note, this issue was explicitly discussed at the JCTVC L meeting.

comment:2 in reply to: ↑ 1 Changed 8 years ago by kolya

Replying to kiranmisra:

Note, this issue was explicitly discussed at the JCTVC L meeting.

Here is following quotation from meeting notes:

JCTVC-L0116 High-level parallelism clean-ups [T. Lee, B. Choi (Samsung)]
This document proposes some high-level syntax changes related to dependent slice segment and entry points signalling. In this proposal, the memorization process for context variables for dependent slice segment is proposed to be invoked no matter what the current slice segment type is, and entry point offsets are coded as the decreased value by 1.
Decision (Ed.): The first aspect is just pointing out an error in the text; the "memorization" is necessary to be performed for independent slice segments as well as dependent slice segments.
The second aspect proposes to apply the "_minus1" coding convention for entry_point_offset[ i ] syntax elements. If we don't adopt this, we would probably want to explicitly prohibit the value 0 anyway, which would be a bit strange to do.
Decision (Cleanup): Apply the "_minus1" coding convention for entry_point_offset[ i ] syntax elements.

But for now, even with "_minus1" added, entry_point_offset_minus1[ i ] cannot be lower than 1.

comment:3 Changed 6 years ago by bbross

  • Resolution set to wontfix
  • Status changed from new to closed

It was agreed that 1-byte slice segments don’t make sense due to CABAC initialization. However, for those cases where it is not easy to figure out the "real" least value, it is sufficient to give a less restrictive value range. Therefore, this ticket can be closed without an action.

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