Of itu-t sg16 wp3 and iso/iec jtc1/SC29/WG11

JCTVC-M0264 AHG9: On some fundamental concepts in HEVC 3DV and scalable extensions [Y.-K. Wang, J. Chen, Y. Chen (Qualcomm)]

This document discusses some fundamental concepts in HEVC 3DV and scalable extensions, including picture, access unit (AU), coded video sequence (CVS), and bitstream. In particular, it proposed for

• 
  AU to be defined to consist of all "elemental pictures" that pertain to a particular output time, similarly as in SVC and MVC,
  
• 
  IRAP AU to be defined as an AU for which all "elemental pictures" are IRAP pictures, and IRAP AU shall contain a picture for each layer that has at least one picture in the CVS.
  
• 
  CVS to be defined to consist of AUs starting from an IRAP AU up to but not including the next IRAP AU in decoding order.
  

JCT3V-D0045 contains basically the same content as this document.

This contribution advocated the alternative to the approach advocated in M0201.

M0045 proposed for a "picture" to be one "view component", but for an "access unit" to be all "pictures" with one output time.
Assuming that an AU is a set of contiguous NAL units in bitstream order, there are two relevant technical issues:

• 
  Do we want to allow mixing different layers / view components with the same output time (e.g. for ultra-low-delay)?
  
• 
  Do we want to allow different "GOP" structures for different view components? This is primarily a coding efficiency issue rather than a functionality or application requirement issue.
  

If the answer is 'no' to both issues, it seems like mostly just an editorial question (plus or minus some HRD details).

It was suggested that the first of the above issues seems more important to consider than the second. Having a definition of access unit that is similar in concept to that in AVC would be consistent with that.

For "picture", the group seemed to lean toward the concept that each AVC-style view component is a "picture" and each scalable layer is a different "picture".

It was requested for text to be drafted with this approach – YKW volunteered to coordinate preparation of such text – which was later provided in revision of the document.

Decision: Adopted the definition of AU (with current definition of "picture", which is one layer / view component).

Defer any open aspects of CVS & IRAP definitions for further study.