Coded Video Sequences

Coded Video Sequences

A coded video sequence consists of a series of access units that are sequential(有序的) in the NAL unit stream and use only one sequence parameter set.

每个视频编码序列包含很多access units, 且仅有一个SPS.

Each coded video sequence can be decoded independently of any other coded video sequence, given the necessary parameter set information, which may be conveyed "in-band" or "out-of-band".

利用发送来的parameter set信息(SPS+PPS), 每个视频编码序列独立解码.

A coded video sequence in H.264/AVC consists of a sequence
of coded pictures .
A coded picture can represent either an entire frame or a single field, as was also the case for MPEG-2 video.

视频编码序列由编码图像组成.
编码图像可能是一个完整帧或一场.

Instantaneous Decoding Refresh (IDR)

At the beginning of a coded video sequence is an instantaneous decoding refresh (IDR) access unit.
An IDR access unit contains an intra picture which is a coded picture that can be decoded without decoding any previous pictures in the NAL unit stream, and the presence of an IDR access unit indicates that no subsequent(随后的) picture in the stream will require reference to pictures prior to the intra picture it contains in order to be decoded.

coded video sequence最开始是IDR帧.
IDR之后的图像解码时不会参考IDR之前的图像.
这样可以有效的防治错误扩散.
这里简单说一下: IDR帧一定是I帧 但I帧不一定是IDR帧
只有在coded video sequence开始的I帧才是IDR帧.
其它的就是普通的I帧.

A NAL unit stream may contain one or more coded video sequence.

一个NAL unit stream可能包含一个或多个coded video sequence.

References:
https://en.wikipedia.org/wiki/Network_Abstraction_Layer#Parameter_Sets
http://iphome.hhi.de/wiegand/assets/pdfs/DIC_H264_07.pdf