EP-4740469-A1 - MULTI-LAYER BITSTREAM CONFORMANCE CHECKING AND CORRESPONDING APPARATUS

Abstract

A method for bitstream conformance checking is disclosed. Information representative of a size of pictures contained in a same access unit and associated with a current output layer set is obtained (S500). For a level signaled for the current output layer set, a size of a decoded picture buffer is determined (S502) responsive to the obtained information. Bitstream conformance for the current output layer set is then checked (S504) by comparing the determined size of the decoded picture buffer with a size of the decoded picture buffer required for decoding the current output layer set.

Inventors

• Urban, Fabrice
• MARQUANT, GWENAELLE
• DE LAGRANGE, Philippe
• SALMON-LEGAGNEUR, CHARLES

Assignees

• InterDigital CE Patent Holdings, SAS

Dates

Publication Date

20260513

Application Date

20240625

Claims (16)

1. 1. A method for checking conformance of a bitstream comprising: obtaining (S500) information representative of a sum of the number of luma samples of pictures contained in a same access unit and associated with a current output layer set; determining (S502), for a level signaled for the current output layer set, a size of a decoded picture buffer responsive to the obtained information; and checking (S504) bitstream conformance for the current output layer set by comparing the determined size of the decoded picture buffer with a size of the decoded picture buffer required for decoding the current output layer set.
2. 2. The method of claim 1, wherein obtaining information representative of a size of pictures contained in the same access unit and associated with a current output layer set comprises parsing a syntax element a value of which is equal to said size.
3. 3. The method of claim 1, wherein obtaining information representative of a size of pictures contained in the same access unit and associated with a current output layer set comprises parsing a first syntax element representative of a picture height and a second syntax element representative of a picture width, wherein a product of values of the first and second syntax elements is equal to the size of pictures contained in the same access unit and associated with a current output layer set.
4. 4. The method of claim 1 , wherein checking bitstream conformance for the current output layer set comprises determining the bitstream for the current output layer set is conform in a case where the size of the decoded picture buffer required for decoding the current output layer set is less than or equal to the determined size of the decoded picture buffer.
5. 5. The method of claim 1, wherein the method further comprises determining whether decoding the current output layer set in real-time is possible by comparing a luma sample rate of the signaled level with the obtained information.
6. 6. The method of claim 5, wherein determining whether decoding the current output layer set in real-time is possible by comparing a luma sample rate of the signaled level with the obtained information comprises determining decoding the current output layer set in real-time is possible in a case where the luma sample rate of the signaled level is above the obtained information multiplied by a frame rate.
7. 7. The method of claim 1, wherein the size of the decoded picture buffer required for decoding the current output layer set is parsed from a decoded picture buffer syntax structure.
8. 8. An encoding method comprising: obtaining information representative of a size of pictures contained in a same access unit and associated with a current output layer set; and encoding the obtained information in a syntax structure associated with the current output layer set.
9. 9. A method for checking conformance a bitstream comprising: obtaining per-layer requirements; parsing information for a current output layer set; deriving per output layer set requirements from per-layer requirements using the parsed information for a current output layer set; and checking bitstream conformance for the current output layer set responsive to the derived per output layer set requirements.
10. 10. The method of claim 9, wherein deriving per output layer set requirements from per-layer requirements comprises computing a sum of buffer sizes needed to decode all layers in the current output layer set.
11. 11. The method of claim 9, wherein obtaining per-layer requirements comprises parsing said per-layer requirements from the bitstream.
12. 12. The method of claim 9, wherein obtaining per-layer requirements comprises deriving said per-layer requirements from per output layer set requirements parsed from the bitstream.
13. 13. An apparatus comprising one or more processors and at least one memory coupled to said one or more processors, wherein said one or more processors are configured to perform the method of any one of claims 1-7 or 9-12.
14. 14. An encoding apparatus comprising one or more processors and at least one memory coupled to said one or more processors, wherein said one or more processors are configured to perform the method of claim 8.
15. 15. A computer program comprising program code instructions for implementing the method according to any one of claims 1-7 or 9-12 when executed by a processor.
16. 16. A computer readable storage medium having stored thereon instructions for implementing the method according to any one of claims 1-7 or 9-12.

Description

MULTI-LAYER BITSTREAM CONFORMANCE CHECKING AND CORRESPONDING APPARATUS CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of European Application No. 23306126.6, filed on July 4, 2023 which is incorporated herein by reference in its entirety. TECHNICAL FIELD At least one of the present embodiments generally relates to a method and an apparatus for conformance checking of a multi-layer video bitstream. BACKGROUND To achieve high compression efficiency, image and video coding schemes usually employ prediction and transform to leverage spatial and temporal redundancy in the video content. Generally, intra or inter prediction is used to exploit the intra or inter picture correlation, then the differences between the original block and the predicted block, often denoted as prediction errors or prediction residuals, are transformed, quantized, and entropy coded. To reconstruct the video, the compressed data are decoded by inverse processes corresponding to the entropy coding, quantization, transform, and prediction. Coding standards, such as VVC (Versatile Video Coding), define coding configurations by means of profiles, tiers, and levels. These coding configurations impose operational constraints that limit the coding toolsets and the ranges of coding parameters that an encoder can utilize for the compression of a video. The profile (and associated level and tier) according to which a coded video bitstream is generated by the encoder is signaled to a decoder, for the latter to verify whether computational resources can be allocated for the decoding of that bitstream. Similarly, a multilayer video can be encoded according to a multilayer profile. A decoder conforming to the multilayer profile needs to have the processing power to decode the multilayer video. In principle, for each layer, the full toolset available in the encoder may be used, and so the processing power required of a multilayer decoder may be the sum of the processing power required to decode each layer. However, in practice and based on specific application requirements, a different toolset can be applied to the encoding of each layer to control the processing power required for the decoding of each layer, while maintaining acceptable compression performance. SUMMARY In one implementation, bitstream conformance may be checked. In examples, information representative of a size of pictures contained in a same access unit and associated with a current output layer set may be obtained; for a level signaled for the current output layer set, a size of a decoded picture buffer may be determined responsive to the obtained information ; and bitstream conformance for the current output layer set may be checked by comparing the determined size of the decoded picture buffer with a size of the decoded picture buffer required for decoding the current output layer set. For example, obtaining information representative of a size of pictures contained in the same access unit and associated with a current output layer set may comprise decoding a syntax element a value of which is equal to said size. In other examples, obtaining information representative of a size of pictures contained in the same access unit and associated with a current output layer set may comprise parsing a first syntax element representative of a picture height and a second syntax element representative of a picture width, wherein a product of values of the first and second syntax elements is equal to the size of pictures contained in the same access unit and associated with a current output layer set. In an example, the size of the decoded picture buffer required for decoding the current output layer set may be parsed from a decoded picture buffer syntax structure. In yet another example, it may be determined whether decoding the current output layer set in real-time is achievable by comparing a luma sample rate of the signaled level with the obtained information. In other examples, per-layer requirements may be obtained ; information for a current output layer set may be parsed ; per output layer set requirements may be derived from per-layer requirements using the parsed information for a current output layer set ; and bitstream conformance may be checked for the current output layer set responsive to the derived per output layer set requirements. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a block diagram of a system within which aspects of the present embodiments may be implemented; FIG. 2 illustrates a block diagram of an embodiment of a video encoder; FIG. 3 illustrates a block diagram of an embodiment of a video decoder; FIG. 4 is a diagram illustrating a multilayer encoding/ decoding workflow; FIG. 5 A depicts a flowchart of a decoding method according to a specific embodiment; FIG. 5B depicts a flowchart of an encoding method according to a specific embodiment; FIG. 6 depicts a flowchart of a decoding method with syntax change according to a spe