HL syntax for range extensions and single-layer HEVC coding

HL syntax for range extensions and single-layer HEVC coding

This contribution proposes a modification to the syntax of current HEVC in order to embed thumbnail video into HEVC bitstreams. A thumbnail video, which is a sequence of snapshots with smaller resolution, is required in many video applications to give a preview of the video content. To support this feature, three modifications are applied to the high level syntax of HEVC. Firstly, a new VCL NAL unit type is proposed to contain the coded thumbnail picture. Secondly, a new SEI message is added to transmit auxiliary information, e.g. the period of presentation of the thumbnails. Finally, a reserved bit in profile_tier_level() structure is changed into a flag to signal the on/off of the thumbnail video in a bitstream. These modifications reportedly do not violate the conformance requirement of current HEVC, and provide a flexible method to enclose the thumbnail information into regular HEVC bitstream.

Using an all-intra VCL NALU was proposed.

Thumbnail alignment to POC was suggested.

It was commented that auxiliary pictures seems like a good alternative approach, perhaps accompanied by SEI.

Further study was encouraged, particularly focused on the auxiliary pictures approach.

15.0.0.1.1.1.1.1.353JCTVC-N0269 HLS: Non-significant slice segments with tiles for single layer HEVC extensions [C. Auyeung (Sony)]

The motion-constrained tile sets SEI message in Range Extensions text specification: Draft 3 can be used to signal that a CVS is comprised of one or more regions of interest in the form of independently decodable motion-constrained tile sets. A user can interactively select and decode a motion constrained tile set without decoding the other tiles. This contribution proposes syntax and semantics that support the extraction of independently decodable motion-constrained tile sets to form a new bitstream without transcoding at the CTU level for streaming of the regions of interest in applications such as interactive UHDTV application, dynamic high-quality zoom-in application, interactive on-demand, e-learning, smart surveillance, and etc.

A prior relevant idea was presented in M0277 and M0046.

Proponent describes replacing regions outside an ROI set of tiles with blank/filler coded picture regions.

As proposed, this would require a new profile.

It was remarked that alternatives to non-backward-compatible syntax may be feasible for this. An SEI message can indicate that some slices would decode as empty.

An analogy was drawn with the pseudo-monochrome indicator at the SPS/VUI level.

Further study is encouraged.

15.0.0.1.1.1.1.1.354JCTVC-N0063 REXT/MV-HEVC/SHVC HLS: Auxiliary picture layers [M. M. Hannuksela (Nokia)]

This contribution proposes to specify new scalability dimension in the VPS extension syntax for a layer carrying auxiliary pictures. It is asserted that the proposed approach:

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  Enables to indicate CPB HRD parameters separately for the primary pictures (i.e., the base layer) and for the entire bitstream;
  
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  Enables to the bitstream extraction process to extract the bitstream containing the primary pictures only;
  
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  Can be used in systems functionalities, such as session negotiation, as the presence of auxiliary pictures is indicated through the VPS; and
  
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  Does not require any new VCL NAL unit type(s).
  

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  Indicating the type and characteristics of auxiliary pictures in the SPS extension.
  
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  Indicating the type and characteristics of auxiliary pictures in an SEI message.
  
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  Indicating the type of auxiliary pictures in the VPS extension and the characteristics in an SEI message.
  

It was remarked that the scheme is quite interesting and seems like a good idea. It was agreed to consider this as a starting point for strong consideration and further development in AHGs on SHVC HLS and RExt. The proponent indicated that software could be provided and this was encouraged.

15.0.0.1.1.1.1.1.355JCTVC-N0077 AHG 5: On support for alpha channel in HEVC [M. Naccari, M. Mrak (BBC)]

Alpha channel signals are used in professional (studio) video coding applications and their usage may become popular also for frame composition at the receiver side. Briefly, the alpha channel complements the information contained in the main bitstream by providing, for each image pixel, its degree of transparency. To support the coding and embedding of alpha channel in the range extensions of the HEVC standard, this contribution introduces the concept of auxiliary picture. An auxiliary picture is a picture which is sent together with the primary coded picture and is compressed and managed as a monochrome picture coded with the same coding tools specified in the syntax of the HEVC standard. In this document, proposed definitions, syntax and semantics for the proposed auxiliary pictures are introduced first and then different options, to address different application requirements, are proposed and discussed.

The contribution proposes the use of LTRPs for repetition, and proposes thresholding values for opaque/transparent determination. The topic was agreed to be for further study in AHGs on SHVC HLS and RExt.

4. HL syntax in SHVC and 3D extensions

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