MpegTS流及PS流区别.doc

IP数据报有首部和数据两部分组成的，首部的前一部分是固定长度20字节，是所有IP数据报必须具有的。首部包括：总长度、标识、MF、DF、片偏移。 
在MPEG-2系统中，信息复合/分离的过程称为系统复接/分接，由视频，音频的ES流和辅助数据复接生成的用于实际传输的标准信息流称为MPEG-2传送流（TS：TransportStream）。 
据传输媒体的质量不同，MPEG-2中定义了两种复合信息流：传送流（TS）和节目流（PS：ProgramStream） 
TS流与PS流的区别在于TS流的包结构是固定长度的，而PS流的包结构是可变长度的。 
PS包与TS包在结构上的这种差异，导致了它们对传输误码具有不同的抵抗能力，因而应用的环境也有所不同。TS码流由于采用了固定长度的包结构，当传输误码破坏了某一TS包的同步信息时，接收机可在固定的位置检测它后面包中的同步信息，从而恢复同步，避免了信息丢失。而PS包由于长度是变化的，一旦某一PS包的同步信息丢失，接收机无法确定下一包的同步位置， 就会造成失步，导致严重的信息丢失。因此，在信道环境较为恶劣，传输误码较高时，一般采用TS码流；而在信道环境较好，传输误码较低时，一般采用PS码流。 
由于TS码流具有较强的抵抗传输误码的能力，因此目前在传输媒体中进行传输的MPEG-2码流基本上都采用了TS码流的包格

MPEG-2 PS是为在存储介质保存视频信息而开发的。而MPEG-2 TS是为在网络传输视频信息而开发的。目前，MPEG-2 TS最广泛地应用是DVB系统。因为IPTV的原因，也作为一种相当普通的视频封装格式。

下面是网络上的一个标准的解析：
It is very important to point out that "Program Stream" has a very specific meaning. MPEG-2 has two different multiplexing schemes: Program Stream and Transport Stream.  The Program Streams are mostly used in storage applications.  Broadcast usage commonly uses the Transport Stream format.  If you have  one content channel (one program), it does NOT imply that the stream that carries the program would be a Program Stream.  In broadcast usage it would be a so-called Single Program Transport Stream (as defined by ISO 13818-1): a multiplexed collection of concatenated Program Streams without beginning or end.  VBrick currently only supports Transport Stream which is superior to Program Stream for streaming applications.
· An MPEG-2 Program Stream contains one, and only one, content channel.  A Program Stream is like a single-passenger car without shock absorbers: drive it on a smooth road.

· An MPEG-2 Transport Stream can contain one or more content channels. A Transport Stream is like a high end car or bus: it can carry one or more passengers and has a good suspension system that can handle the bumps in the road.  VBrick supports Single Program Transport Stream, so this is like a single passenger car with good suspension.
MPEG-2 Multiplexing
The MPEG-2 standard allows two forms of multiplexing:
· MPEG Program Stream A group of tightly coupled PES packets referenced to the same time base. Such streams are suited for transmission in a relatively error-free environment and enable easy software processing of the received data. This form of multiplexing is used for video playback and for some network applications.

· MPEG Transport Stream Each PES packet is broken into fixed-sized transport packets forming a general purpose way of combining one or more streams, possibly with independent time bases. This is suited for transmission in which there may be potential packet loss or corruption by noise, or / and where there is a need to send more than one program at a time.