Differences between IASA and TS

Prior to the establishment of Isma, the active image expert group defined the reuse of one or more audio, video, and data element streams when developing MPEG-2 system standards

Method, MEPG-2 standards were officially released in November 1994. The data stream is packaged with a time mark to form a encapsulated element stream (PES ). Audio

, Video and data (optional) PES are reused together to form a single output stream that can store and transmit applications. MPEG-2 system standards are designed to provide

Syntaxes are required to synchronize audio and video declaration information. The MPEG-2 system standard has program flow (PS) and transmission flow (TS) two kinds of data flow:

• A Variable Length package for PS and a short fixed size package for ts.

• PS is usually used in DVD storage applications, and Ts is usually used in scenarios where many errors occur.

• Ts reuses data streams that do not have a common time benchmark. The fixed length is l88 bytes. The 188-byte package contains at least 4 bytes.

It is used as the header and other bytes for data transmission and storage, audio and video information. The ts header command contains the following information: synchronization, package private, program id, and

Error status. TS can contain the time information provided by the header field.

Like Isma stream, MEPG-2 TS Stream is a data stream format that transmits video and audio signals in the Internet environment.

Format.

From the development history of the above two streams, Isma has a relatively short history, which is only a standard for streaming media services on the Internet.

Pc vod is widely used, but it is rarely used in the Digital Video Broadcast Field Based on broadband networks and television terminals.

Low Bit Rate on-demand programs and low concurrency rates.

TS Stream is a common standard in the broadcast industry. It has been widely used for more than a decade. It is designed for broadband-based digital video broadcast.

It supports a variety of basic media streams and multiple media encoding standards, and is recognized by the global broadcast industry and the Internet industry. At present, China Netcom IPTV preliminary

The specification clearly requires that TS stream formats be supported during transmission.

From the perspective of the purpose of flow standards, the Isma flow is designed to promote the application of MEPG-4, so the design of the whole system

Is around the MEPG-4, its stream format is related to media files, it is designed to optimize the MEPG-4 File Transfer in the network. To optimize the system

DESIGN: apart from the encoder and decoder of the terminal, you need to know the details of the/V codec (such as the video format,

Streaming Media Servers also need to understand the coding and decoding details (such as video formats), so that the entire system can make corresponding

Optimization, which will inevitably increase the load of streaming media servers. The MEPG-2 TS Stream format is irrelevant to the media itself, that is, the TS stream is only responsible

To transfer a media file, you only need to know the/V encoding of the encoder and decoder that import the media file into the system.

Decoding details (such as video formats) are not required by other servers (such as streaming media servers. So although the TS Stream format is in MEPG-2

Defined, but it can also be used to pass the media file of the MEPG-4, just because it is defined in the MPEG-2, so it is often called the MEPG-2 TS stream.

In terms of media processing methods, from the encoding end to the decoding end, we need to establish multiple RTP for audio and video and other data streams.

Session. Therefore, when I/O is used as a streaming media server, you need to manage multiple input and output, multiple buffer management, and synchronization between them.

It greatly increases the processing capability of the Streaming Media Server, brings great algorithm complexity, and reduces the stability and reliability of the system. Just

Is the Isma MP4 File Header Format. Using the Isma standard requires more RTP sessions to be managed, and more I/O and buffer to be managed, which will greatly eliminate

It consumes the CPU performance and memory of the Streaming Media Server and STB, seriously affecting the system performance. According to the Darwin System and Its experiments

On the performance machine, only a few streams can be run and the disconnection may occur. Isma's video and audio synchronization relies on the time stamp in RTP.

Therefore, in the same step, you must wait until the RTP of the audio and video arrive to synchronize the video and audio. The result is that Isma is used to make the network unstable.

The synchronization time may increase, resulting in insufficient response to operations such as channel switching and fast forward and fast return. In addition to the decoder

The Streaming Media Server needs to be involved in AV synchronization, which consumes resources of the Streaming Media Server, increases algorithm complexity and performance costs, and reduces

System reliability and stability. When Isma is used for decoding, multiple RTP Session connections need to be established, so Multiple Buffer

And manage it. Therefore, the memory and CPU resources of the decoder used when Isma is used are more, and the hardware requirements are higher. It is precisely because TS

The stream and media format are irrelevant. No matter what new media format is used, it does not affect the Streaming Media Server.

The synchronization of audio video streams without a common time benchmark is provided by the TS header, So audio and video synchronization does not require the participation of streaming media servers,

Simplified the design of streaming media servers.

From the processing method, multiple audio and video streams and other data streams must be reused. Only one RTP session needs to be established. Therefore, I/O and Buffer

Processing and audio/video synchronization will be much simpler and easier. Using TS stream, the Streaming Media Server will support several hundred 2 m

And will not be dropped. In terms of video and audio synchronization, TS does not have the same problem as Isma, because its time information is in a stream.

The video and audio synchronization only needs to be implemented at the encoding and decoding end. other links in the middle, such as the streaming server, can reduce the Streaming Media Server.

Algorithm and processing complexity. In terms of decoding, the main task of TS stream is to demultiplexing, that is, the demultiplexing needs to analyze the PSI information, and then according to the PSI

Information is used to obtain the audio and video PID. The video and audio streams are obtained through PID filtering and output to their respective buffer. Because ts is a fixed 188-byte packet structure

Therefore, the position of PID in the package is fixed, and the filter is easy to implement. After testing, the software TS Stream de-multiplexing method is adopted in the Equator BSP-15 platform.

The CPU usage is less than 5%, and the hardware requirement of the set-top box is also lower than that of the Isma format.

In terms of service support, channel switching is a key indicator. The Isma method is used to switch live TV channels.

A lot of information is required in the Isma file header, so STB needs to re-obtain the Isma file header from the system. Therefore, the system must have a complete set of Isma

File Header generation and management. This will cause a delay in switching the decoding channel. The Isma method is used. When live TV performs channel switching, STB also needs

The new SDP is obtained and the audio and video session is re-established. Both of these two aspects will result in a long channel switching time and cannot meet the requirements of the Telecom standard for 2 seconds.

These two factors lead to slow Isma channel switching. During live TV, if the parameters of the encoder are modified

STB re-establishes an RTSP session with the encoder or streaming media server to obtain the new SDP, and then obtains the one required for decoding from SDP.

Specific parameters. The TS Stream does not have a so-called file header, and the audio and video are also in the same stream. Therefore, channel switching can be achieved quickly, meeting the requirement of 2

The second switching time requirement. When the channel parameter is changed, all the decoding parameters come along with the bitstream, so no need to create

Set another session, and the decoder will respond faster.

Network technology and computer technology are developing very rapidly, so system upgrades are inevitable: support for different encoding formats need to be upgraded, adding new achievements

Yes, you need to upgrade your services. Isma1.0 Video Based on MPEG-4 Part2, based on SP and ASP, not involved

H.264, whereas isma2.0 is Based on H.264. isma2.0 is not compatible with isma1.0. That is, isma1.0 servers and clients cannot be smoothly upgraded to isma2.0.

System:

1. The encapsulation mode of the video RTP package is incompatible;

2. The DP Message format is incompatible;

3. File Storage Method inconsistent: isma1.0 Based on MPEG-4 part14 (*. MP4), while isma2.0 file format based on MPEG-4 part15

(*. Avc1 ).
Currently, isma2.0, which supports H.264, has just been released and has not received many support from professional encoders.

The storage of TS is irrelevant to the media encoding format, and MPEG-2 ts can encapsulate content in any format. When you store ts streams, you only need to segment them.

Processing, add the index information, and store it together with the TS stream. Therefore, the use of TS Stream file formats has better compatibility and convenience for the IPTV Platform

. For H.264 support, many H.264 professional encoders are currently supported, such as tandberg and harmonic.

IPTV systems need to provide commercial operations and are very concerned about digital copyright management. Although DRM uses the AES encryption method, Isma does not

Scalability. It does not support multiple DRM methods and encryption standards, and does not support key management. While TS has solved the above problems, you can

The key management method and ing relationship are defined in the RTP extension, and different DRM methods and standards make the system have a wide range of DRM

Compatibility.

The key to IPTV success lies in content. In this respect, TS has advantages.

At present, most of the CP are television stations, film companies and television companies, their main sources are using MPEG-2 TS Stream Encapsulation Format. Therefore, TS can

Well adapt to the main status quo and needs of CP. In terms of compatibility with DVB (digital video broadcast ),

In the electrical field, DVB uses the TS Stream Encapsulation Format. Therefore, if ts is used, it will be fully compatible with DVB programs in the radio and television field in the future. While Isma streams

You must use transcoding to import the content.

Currently, all Professional encoder manufacturers only support ts, but not Isma, such as harmonic,

Tandberg, scientific atlanta, etc., all the MPEG-4 and H.264 decoding chip support ts format, so select ts can be STB (

Set-Top-box set-top box) provides more options to help reduce the cost of STB. Most of the IPTV systems that are already running abroad

MEPG-2 ts format, including France Telecom, PCCW, Yahoo! BB and other mainstream operators.

From the above comparison we can see that the difference between Isma stream and MEPG-2 TS stream is designed for different applications, Isma stream is

Under the Internet computer environment development, can make up for the network quality through the computer performance, while MEPG-2 is more consider in the broadcast industry application environment

If the stream transmission is optimized. The stream format reflects the application model taken into account in system development.