視訊處理

Breif Description of nal_ref_idc Value in H.246 NALU

I am so sorry for my late update because of my study!
A quite update of myself: I have actually stopped working on H.264 and MP4 for some time but will probably pick up again in the near future.

As in the article Introduction to H.264: (1) NAL Unit, Suji Mani asked what is the exact meaning of different values in nal_ref_idc. In fact, nal_ref_idc is base on “Start Code Value” and represents the priority of the current frame (i.e. how important of the frame – the higher the value, the more important the frame). Here is a list of nal_ref_idc values with the corresponding Start Code Type:
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Introduction to H.264: (2) SODB vs RBSP vs EBSP

Here is a summary of the relationship between SODB, RBSP, EBSP, NALU and H.264 Byte Stream.
SODB: String of Data Bits
RBSP: Raw Byte Sequence Payload
EBSP: Encapsulate Byte Sequence Payload

SODB + RBSP Stop bit + 0 bit(s) => RBSP

RBSP part 1 + 0x03 + RBSP part 2 + 0x03 + … + RBSP part n => EBSP

NALU Header + EBSP => NALU

In Byte Stream Format (Annex B),

Start CodeNALU + … + Start CodeNALU => H.264 Byte Stream

String of Data Bits (SODB)

Definition:

3.149  string of data bits (SODB): A sequence of some number of bits representing syntax elements present within a raw byte sequence payload prior to the raw byte sequence payload stop bit. Within an SODB, the left-most bit is considered to be the first and most significant bit, and the right-most bit is considered to be the last and least significant bit.

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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.

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免費下載:H.264和MP4文件格式的標準/規範 官方文件

注意!這些官方文件只有英文版!

對於要學習 H.264 和 MP4 文件格式的人來說,看懂官方的標準/規範是十分重要的。以下是有提供免費下載的鏈接:

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

ITU-T 和 ISO 網站中均有提供。在ITU-TH.264 被分類在 Series H: Audiovisual and multimedia systems 中而在ISO,它是在ISO/IEC 14496 (MPEG-4)中(Part 10)。如果要學習H.264和MP4的關係,Part 15也有參考價值,但需付費購買。

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


暫無中文版

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.

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