NAL Unit Type for Open GOP Encoding in Interlaced Video

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Solution Overview

Problem

In the HEVC encoding scheme, when a picture forming a field pair with an intra picture constitutes a random access point, it is not possible to insert a leading picture, thereby preventing the encoding of an open Group of Pictures (GOP).

Innovation Solution

By setting the NAL unit type of a slice of encoded image data to a unique type indicating a picture dependent on the intra picture, allowing an LP to be inserted as a succeeding picture, thus enabling the encoding of an open GOP.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a picture forming a field pair with an intra picture constituting a random access point is set to a trailing picture (TP), then the encoding structure is simplified, but it becomes impossible to insert a leading picture (LP) and thus impossible to encode an open Group of Pictures (open GOP)

Engineering Contradiction:

Improveencoding structureVSAvoidopen GOP encoding capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent introduces a new NAL unit type parameter (RAP_dependent) to change the classification of pictures forming field pairs with intra pictures. Instead of being strictly classified as trailing pictures (TP), these pictures can now be marked with the RAP_dependent type, which allows them to serve as reference pictures for leading pictures (LP) while maintaining their dependency relationship. This parameter change enables the encoding structure to support open GOP without increasing complexity.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If a unique NAL unit type is introduced to indicate pictures dependent on intra pictures, then open GOP encoding becomes possible, but the NAL unit type complexity increases

Engineering Contradiction:

Improveopen GOP encoding capabilityVSAvoidNAL unit type

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The RAP_dependent NAL unit type serves multiple functions: it indicates pictures that form field pairs with intra pictures, establishes reference relationships for leading pictures, and maintains compatibility with existing HEVC decoding structures. By making this NAL unit type multi-functional, the patent achieves open GOP encoding capability without proportionally increasing overall system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP3038365B1Encoding device, encoding method, transmission device, decoding device, decoding method, and reception device

Publication Date: 2021.01.13 SONY GROUP CORP

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AI summary

To enable image data of the interlacing scheme to undergo encoding of an open GOP. An image encoding unit encodes image data of each picture constituting image data in an interlacing scheme in an NAL unit structure and generates a video stream having the encoded image data of each picture. The image encoding unit sets an NAL unit type of a slice of encoded image data of a picture forming a field pair with an intra picture constituting a random access point to a unique type which indicates a picture that is dependent on the intra picture and forms the field pair with the intra picture.