Tag Archive: Standard / Specification

International Standard / Specification, like ISO, ITU-T, IEEE…

Introduction to H.264: (1) NAL Unit

H.264 / MPEG-4 Part 10, Advanced Video Coding (MPEG-4 AVC) is a common video compression format developed by ITU-T Video Coding Experts Group (VCEG) and ISO/IEC JTC1 Moving Picture Experts Group (MPEG). Network Abstraction Layer (NAL) and Video Coding Layer (VCL) are the two main concepts in H.264. A H.264 file consists of a number of NAL units (NALU) and each NALU can be classified as VCL or non-VCL. Video data is processed by the codec and packed into NAL units.

NALU in Packet-Transport Protocol V.S. Byte-Stream Format

There are two ways to pack a NAL unit for different systems, Packet-Transport System and Byte-Stream Format. For Packet-Transport systems like RTP, the transport system protocol frames the coded data into different pieces. Hence, the system can easily identify the boundaries of NAL units and we don’t need to add extra start code, which is a waste of resources. This method is usually used in streaming.


Free Download: H.264 and MP4 file format Standard / Specification

Studying the standard is very important for learning H.264 and MP4 container format. Here are the download links of the free official documents.

H.264 (MPEG-4 Part 10 / MPEG-4 AVC), Advanced Video Coding

It is available on both ITU-T and ISO website. H.264 is in Series H: Audiovisual and multimedia systems in ITU-T while it is in Part 10 of ISO/IEC 14496 (MPEG-4) in ISO. If you need to study the relationship between H.264 and MP4 container, you should also refer to Part 15 (not free).


Explanation of Descriptors in the ITU-T Publication on H.264 Coding Standard / Recommendation (with example)

This text will be displayed in English

I have started to learn H.264 for a week. My job required me to decode some H.264 video clips streamed from a media processor Hi3518 manufactured by Hisilicon. Yet, I have no background in video coding and it is a hard time for me now. I will keep writing and organizing the related materials for my revision and also for your reference. In this section, I am going to explain the descriptors used in the ITU-T official Publication on H.264 Coding Recommendation: Advanced video coding for generic audiovisual services and illustrate with some example. It is the basic thing you need to understand first before you could understand how to decode a H.264 video clip. There are 10 main descriptors, which are as follows (extracted from the document, edition 2013):

The following descriptors specify the parsing process of each syntax element. For some syntax elements, two descriptors, separated by a vertical bar, are used. In these cases, the left descriptors apply when entropy_coding_mode_flag is equal to 0 and the right descriptor applies when entropy_coding_mode_flag is equal to 1.