What Is TS Or Transport Stream MPTS SPTS For Digital Headend System
When the things comes in terms of Digital Headned then MPEG TS plays an important role in it. MPEG stands for Moving Picture Expert Group. MPEG TS is a standard used to send MPEG video and audio over the DVB (Digital Video Broadcasting). This MPEG video and audio known as program data.
So If you are working for a Digital Video Broadcasting system then you have to go threw MPEG TS.
What Is TS
TS is Abbreviated for Transport Stream. TS contains one or more programs. These programs are in the packets. Thus these programs contain Tables. These tables can be like PAT.
We need to allocate a unique IP address to each transport stream with the UDP port. By using this unique IP and UDP port we can play transport streams in TS Reader and VLC Player , if encryption of programs is not done. We can also record transport streams in computer by using these softwares.
Above shown figure defines the generation of a Transport Stream. Where two encoder are used to encode video and audio signals as input. A mux is used to multiplex and generate TS as output. This TS MUX provides IP output.
There are two types of Transport Streams
(1) SPTS
SPTS is known as Single Program Transport Stream. A transport stream which contains single program in it is known as SPTS.
What Is Elementary Stream
(2) MPTS
MPTS is known as Multi Program Transport Stream. This type of transport stream can contain multiple programs in it. So it called as MPTS.
These transport streams can have two type of bit rates like VBR and CBR. VBR is known as Vairable Bit Rate and CBR is known as Constant Bit Rate.
Basically a transport stream provides a VBR. But some null packets are inserted in to provide Constant Bit Rate. Because for a digital headend if a transport stream is giving VBR it means its bitrate is varying that can produce freezing in the services. To avoid these kind of issues we define maximum bit rate to the encoders for SPTS.
The reserved PID for null packet is 0x1FFF. null packets are also known as empty packets. If we want to convert a stream from VBR to CBR then we have to remove these null packets.
As discussed above a TS contains the packets. These packets are of 188 bytes. This size can be extended to 204 bytes if a Error Correction Code is added.
The TS packet contains following things in it
The value of sync byte is 0x47. It is used to indicate the starting of the header. It is first byte of the header. There is adaption field which contains the data that do not have the Transport stream packets. The payload data contains Meta Data as well as video and audio data.
Adaption field mainly contains the PCR known as Program Clock Reference timestamp. PCR is used to define the time of steam.
Conclusion Of Transport Stream
A transport stream plays an important role in term of Digital Video Broadcasting. A Transport Stream contains different Programs in it. We can record and play these programs by disabling encryption. The PSI SI Tables are also send with the Transport Streams to the STB. Which makes easy to read for the STB to tune the Transport Streams for different parameters.
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