BACKGROUND

1. Field

Methods and apparatuses consistent with embodiments relate to video coding and decoding, and more particularly, a method and an apparatus for signaling one or more independent picture headers and one or more dependent picture headers in an access unit of a coded video sequence.

2. Description of Related Art

Video coding and decoding using inter-picture prediction with motion compensation has been known for decades. Uncompressed digital video can consist of a series of pictures, each picture having a spatial dimension of, for example, 1920×1080 luminance samples and associated chrominance samples. The series of pictures can have a fixed or variable picture rate (informally also known as frame rate), of, for example 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080 luminance sample resolution at 60 Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of such video requires more than 600 GByte of storage space.

One purpose of video coding and decoding can be the reduction of redundancy in the input video signal, through compression. Compression can help reducing aforementioned bandwidth or storage space requirements, in some cases by two orders of magnitude or more. Both lossless and lossy compression, as well as a combination thereof can be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between original and reconstructed signal is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely employed. The amount of distortion tolerated depends on the application; for example, users of certain consumer streaming applications may tolerate higher distortion than users of television contribution applications. The compression ratio achievable can reflect that: higher allowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broad categories, including, for example, motion compensation, transform, quantization, and entropy coding, some of which will be introduced below.

The concept of dividing a coded video bitstream into packets for transportation over packet networks has been in use for decades. Early on, video coding standards and technologies were in their majority optimized for bot-oriented transport, and defined bitstreams. Packetization occurred in system layer interfaces specified, for example, in Real-time Transport Protocol (RTP) payload formats. With the advent of Internet connectivity suitable for mass-use of video over the Internet, the video coding standards reflected that prominent use case through the conceptual differentiation of a video coding layer (VCL) and a network abstraction layer (NAL). NAL units were introduced in H.264 in 2003, and have been retained in certain video coding standards and technologies since then with only slight modifications.

A NAL unit can, in many cases, be seen as the smallest entity on which a decoder can act upon without necessarily having decoded all preceding NAL units of a coded video sequence. Insofar, NAL units enable certain error resilience technologies as well as certain bitstream manipulation techniques, to include bitstream pruning, by Media Aware Network Elements (MANEs) such as Selective Forwarding Units (SFUs) or Multipoint Control Units (MCUs).

FIG. 1depicts relevant parts of the syntax diagram of NAL unit headers in accordance with H.264 (101) and H.265 (102), in both cases without any of their respective extensions. In both cases, the forbidden_zero_bit is a zero bit used for start code emulation prevention in certain system layer environments. The nal_unit type syntax element refers to the type of data a NAL unit carries, which can be, for example, one of certain slice types, parameter set types, Supplementary Enhancement Information (SEI) message, and so on. The H.265 NAL unit header further comprises nuh_layer_id and nuh_temporal_id_plus1, which indicate the spatial/SNR and temporal layer of a coded picture the NAL unit belongs to.

It can be observed that the NAL unit header includes only easily parseable fixed length codewords, that do not have any parsing dependency to other data in the bitstream such as, for example, other NAL unit headers, parameter sets, and so on. As NAL unit headers are the first octets in a NAL unit, MANEs can easily extract them, parse them, and act on them. Other high level syntax elements, for example slice or tile headers, in contrast, are less easily accessible to MANEs as they may require keeping parameter set context and/or the processing of variable length or arithmetically coded codepoints.

It can further be observed that the NAL unit headers as shown inFIG. 1do not include information that can associate a NAL unit to a coded picture that is composed of a plurality of NAL units (such as, for example, comprising multiple tiles or slices, at least some of which being packetized in individual NAL units).

Certain transport technologies such as RTP (RFC 3550), MPEG-system standards, ISO file formats, and so on, may include certain information, often in the form of timing information such as presentation time (in case of MPEG and ISO file format) or capture time (in case of RTP) that can be easily accessible by MANEs and can help associating their respective transport units with coded pictures. However, the semantics of these information can differ from one transport/storage technology to another, and may have no direct relationship with the picture structure used in the video coding. Accordingly, these information may be, at best, heuristics and may also not be particularly well suited to identify whether or not NAL units in a NAL unit stream belong to the same coded picture.

The conventional video syntax redundantly signals parameters referenced by one or more slices or VCL NAL units.

SUMMARY

According to embodiments, a method of reconstructing in a decoder a coded enhancement layer picture, is performed by at least one processor and includes decoding at least one independent picture header of a coded picture of a reference layer, the coded picture of the reference layer being referenced by the coded enhancement layer picture, and decoding a dependent picture header of the coded enhancement layer picture. The method further includes performing picture header prediction including either one or both of predicting at least one value of at least one syntax element of the dependent picture header from at least one value of at least one corresponding syntax element of the at least one independent picture header; and inferring at least one value of a non-present syntax element of the dependent picture header to be equal to at least one value of a present syntax element of the at least one independent picture header.

According to embodiments, an apparatus for reconstructing in a decoder a coded enhancement layer picture, includes at least one memory configured to store computer program code, and at least one processor configured to access the at least one memory and operate according to the computer program code. The computer program code includes first decoding code configured to cause the at least one processor to decode at least one independent picture header of a coded picture of a reference layer, the coded picture of the reference layer being referenced by the coded enhancement layer picture, and second decoding code configured to cause the at least one processor to decode a dependent picture header of the coded enhancement layer picture. The computer program code further includes performing code configured to cause the at least one processor to perform picture header prediction including either one or both of predicting at least one value of at least one syntax element of the dependent picture header from at least one value of at least one corresponding syntax element of the at least one independent picture header, and inferring at least one value of a non-present syntax element of the dependent picture header to be equal to at least one value of a present syntax element of the at least one independent picture header.

According to embodiments, a non-transitory computer-readable storage medium stores instructions that cause at least one processor to decode at least one independent picture header of a coded picture of a reference layer, the coded picture of the reference layer being referenced by the coded enhancement layer picture, and decode a dependent picture header of the coded enhancement layer picture. The instructions further cause the at least one processor to perform picture header prediction including either one or both of predicting at least one value of at least one syntax element of the dependent picture header from at least one value of at least one corresponding syntax element of the at least one independent picture header, and inferring at least one value of a non-present syntax element of the dependent picture header to be equal to at least one value of a present syntax element of the at least one independent picture header.

