h264创意比特流是如何组织的?/头开始代码 [英] How is a h264 idea bitstream organized? / header start codes

问题描述

我试图通过使用十六进制编辑器查看视频文件的比特流来学习一些有关h264的知识.我在此处找到了视频对象平面的起始代码( 0x000001b6)和i帧(0x000001b600).

I was trying to learn a bit about h264 by looking at the bitstream of a video file with a hex editor. I found here the start codes for a video object planes (0x000001b6) and for i-frames (0x000001b600).

但是我在视频文件中找不到很多这些字节.多数情况下，这些起始代码出现在文件的开头，中间只有几处.我希望它们在整个文件中以均匀的距离非常规律地显示！?

But I can't find many of those bytes in video files. Most of the time those start codes appear at the beginning of a file with only a few bites in between. I expected them to show up very regularly, in equal distance all over the file!?

这样用十六进制编辑器查看文件是否还可以?还存在其他哪些起始代码，以及如何组织h264文件?

Is is even ok to look at a file with a hex editor this way? What other start codes exist and how is a h264 file organised?

推荐答案

0x000001b6起始代码适用于mpeg-4第2部分视频，这是简单的配置文件.这对应于编解码器，例如XVID和DIVX. H.264是mpeg-4第10部分，它是高级视频编码配置文件. H.264使用不同的起始代码.

The 0x000001b6 start code applies to mpeg-4 part 2 video which is the simple profile. This corresponds to codecs such as XVID and DIVX. H.264 is mpeg-4 part 10 which is the advanced video coding profile. H.264 uses different start codes.

我对第10部分的熟悉程度不如对第2部分的熟悉程度，但是对标准(ISO 14496-10)的简要了解表明，比特流被分成了称为NAL单元的部分.这些单元前面有24位代码0x000001，以按照B.1.1节进行同步.根据第7.3.1节，以下字节由字段forbidden_zero_bit，nal_ref_idc和nal_unit_type组成.

I am not as familiar with part 10 as I am with part 2, but a brief look through the standard (ISO 14496-10) shows that the bitstream is broken into sections called NAL units. These units have the 24 bit code 0x000001 preceding them for synchronization as per section B.1.1. The following byte is made up of the fields forbidden_zero_bit, nal_ref_idc, and nal_unit_type as per section 7.3.1.

我不确定这些NAL单元是否在帧边界上分开.您可能只需要掌握列出所有比特流语法的标准即可.

I am not sure whether these NAL units are separated on frame boundaries or not. You may just have to get a hold of the standard that lays out all of the bitstream syntax.

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