ST 2073 VC-5 Suite of Standards

OV 2073-0:2023

Overview
The overview describes each of the published documents in the VC-5 standards suite.

ST 2073-1:2017

Elementary Bitstream
The bitstream document defines the syntax and semantics of all VC-5 bitstreams.

A VC-5 bitstream can contain one or more rectangular arrays of integer components with a precision of at most 16 bits each for the width and height. The elementary bitstream standard does not explicitly specify how to encode an image into a VC-5 bitstream. It only provides the framework for specifying how rectangular arrays can be encoded using the VC-5 standards.

RP 2073-2:2022

Conformance Specification
The conformance specification defines how to verify the compliance of an encoder or decoder implementation with the VC-5 standards. This document includes access to the VC-5 test materials: software implementations of the sample encoder and reference decoder and test images and bitstreams for verifying compliance with the VC-5 standards.

The test materials used for conformance testing comprise:

1. Reference decoder for testing bitstreams created by implementations of a VC-5 encoder for compliance with the VC-5 essence standard,
2. Bitstreams and reference images for testing implementations of a VC-5 decoder for compliance with the VC-5 essence standard.

Although not required for conformance testing, the test materials include a sample encoder, the images used by the sample encoder to create the bitstreams used for conformance testing, a program for converting between image formats, and a program for comparing image files. This recommended practice describes the image file formats used by the software and scripts that automate the conformance testing procedure.

Detailed instructions for installing and building the programs and contact information for submitting bug reports are provided in a separate document that is included in the software distribution of the test materials. Access test materials:

ST 2073-3:2015

Image Formats
The image format document specifies how to represent images in a VC-5 bitstream. This standard adds tag-value pairs to represent image-specific information such as the image dimensions and pixel format of the source image.

SMPTE ST 2073-3 introduces the concept of a pattern element: a rectangular subset of component samples in an image corresponding to a single pixel. For example, an RGB image would comprise three component arrays, one for each color component, and each pattern element comprises a single component sample. The concept of pattern element is very useful for describing Bayer images. For example, a pattern element in a typical Bayer image might comprise a 2 by 2 pattern element containing R, G, G, and B color components.

ST 2073-4:2015

Subsampled Color Difference Components
Images can be representing using YCbCr color components. The Cb and Cr components may be subsampled. This standard extends SMPTE ST 2073-3 to describe subsampled color difference components using an extension of the pattern element concept. SMPTE ST 2073-4 adds tag-value pairs that describe the subsampling scheme.

ST 2073-5:2015

Layers
Some images logically comprise multiple images with the same dimensions and pixel format. For example, a stereo pair is two images representing the left and right halves of the stereo pair. Each image has the same dimensions and format. 

This standard adds the capability to represent multiple images in the bitstream, each image having the same dimensions and pixel format. Each individual image is called a layer. 

Applications of layers include stereo pairs, multiple image exposures for HDR, and the top and bottom images in interlaced video.

ST 2073-6:2015

Sections
A VC-5 bitstream is a sequence of tag-value pairs. The reference decoder is a simple state machine that transitions to the next image component or wavelet transform within an image component. Nothing in the VC-5 bitstream explicitly identifies the structure in the sequence of tag-value pairs.

This standard adds tag-value pairs that can be used to delineate semantically relevant portions of the bitstream. For example, section tags can identify each image component within the bitstream or each wavelet transform within a component. 

Sections enable additional capabilities including:

• Identifying portions of the bitstream that can be decoded concurrently,
• Partial decoding and lower resolution decoding,
• Adding error detection and correction to the bitstream.

If image component arrays are delineated using sections, then the decoder can skip components that do not have to be decoded. For example, if the image represented in the bitstream contains Y, Cb, and Cr components and the output image is monochrome, then it is not necessary to decode the Cb and Cr components.

Wavelet transforms are present in the bitstream in order from small (lower resolution) to large (higher resolution). If wavelet transforms are delineated using sections and the output image has reduced resolution, then the larger (higher resolution) transforms can be skipped.

Sections also allow multiple images with different dimensions, formats, and other characteristics to be represented in a single VC-5 bitstream.

ST 2073-7:2022

Metadata
This standard specifies the method for embedding metadata in a VC-5 bitstream.

There are four types of metadata supported by the VC-5 codec:

1. Intrinsic metadata that assist in decoding the images represented by a VC-5 bitstream,
2. Extrinsic metadata defined by other standards,
3. Streaming data, and
4. Dark metadata.

Intrinsic metadata is unique to the VC-5 codec.

Examples of extrinsic metadata include Adobe XMP metadata. The XML representation can be embedded in the VC-5 bitstream and extracted during decoding.

Streaming data is used for time series measurements associated with camera applications such as GPS coordinates and accelerometer readings.

Dark metadata is intended for metadata that does not have a published standard such as vendor-specific metadata.

ST 2073-10:2017

MXF Wrapper
SMPTE uses the Material Exchange Format (MXF) as the container for video and audio tracks.

This standard specifies how to embed a VC-5 bitstream as a video track in an MXF generic container.