Comparison between MPEG2 TS and Isma

Statement 1:

Although Isma and MPEG-2 ts over IP can be used for IPTV stream transmission, but due to the Mechanism and the original intention of different standards, there are some differences in IPTV service support, the specific analysis is as follows:

1. Support for business functions

Isma currently supports MPEG-4 and H.264 and does not support other encoding standards. As video and audio streams are transmitted separately, Isma provides more flexible support for multi-track, multi-subtitle, and other DVD experience features and future interactive scenarios without additional bandwidth resources. As Isma uses existing Internet protocols, Isma provides more flexible support for interactive services. In addition, the Isma protocol stack will support video communication, VoIP, and other traffic services in the future. The Isma protocol stack can also be directly supported in the encapsulation of video and audio data without any extension.

MPEG-2 ts over IP mode is not limited to codec standards, can support MPEG-2/4, H.264 and VC-1 and other codec standards. However, because it is a single first-class transmission after the video and audio streams are reused, the support of MPEG-2 ts over IP for multi-track, multi-word screen and future interactive scenarios needs to encapsulate all stream information in a unified manner, this is a waste of bandwidth that users do not need. If video communication, VoIP and other traffic business, MPEG-2 ts over IP Mode also need to expand to support.

2. Support for Business Performance

Isma introduces the RTP/RTCP protocol, so it can monitor network conditions through RTCP to facilitate QoS Control for services. The receiver synchronizes video and audio data streams using the RTP protocol timestamp. However, because SDP is used to describe the information required for stream creation, when switching live channels, the client needs to re-obtain the SDP file, which may lead to a certain switching latency. The overhead of Isma encapsulation protocols mainly comes from RTP, TCP/UDP, and IP address headers. The overhead is relatively small, resulting in high transmission efficiency. Generally, UDP is used to carry data. If packet loss retransmission measures are not deployed at the application layer, image mosaic may occur when packet loss occurs on the network. The receiving end uses DTS/PTS in the PES package as the decoding and display timestamp. The time information is richer, and the delay of channel switching time mainly comes from the network. Because of the Fixed Length of the packet structure, the MPEG-2 ts over IP Mode needs to occupy more overhead phase, it also leads to lower transmission efficiency than Isma.

In general, Isma's biggest advantage lies in the open standards set for Internet applications. The two-way interaction of the IP network brings more flexibility to support value-added services in the future, the biggest advantage of MPEG-2 ts over IP is maturity, especially suitable for broadcasting business, the support for interactive business needs to be expanded.

It is worth mentioning that although there are still IPTV solutions that use private third-party protocols instead of the above two protocols, their basic idea is to use existing Internet protocols, similar to Isma, but slightly different in implementation.

Statement 2:

1. Comparison of objectives
Isma is only a standard for streaming media services on the Internet. Therefore, Isma aims to provide low-bit-rate on-demand programs and low concurrency rates on the Internet. Ts is a general standard in the media industry. It aims to implement broadband-based digital video broadcast and supports a variety of basic media streams and multiple media encoding standards, it has been widely applied for more than a decade and has been recognized by the global broadcast industry and the Internet industry. Isma has a relatively late history and has a low degree of recognition in the industry. There are no large-scale deployment cases.
2. Compatibility and upgrade of the Streaming Server
A) File Format compatibility
In Isma, different encoding standards have different file formats, such as MPEG-4 and H.264 file formats are different, so there is no compatibility in the file format. While ts storage has nothing to do with the Media Encoding format, MPEG-2 ts can encapsulate any format of content into it. When you store a TS stream, you only need to segment it, add the index information, and store it together with the TS stream. Therefore, the file format using TS stream has better compatibility, which is a perfect solution for smooth upgrade of the IPTV platform.
B) stream format compatibility
I. Isma 1.0/1.1 and Isma 2.0
The system architecture is quite different and difficult to upgrade, mainly manifested in the following aspects:
? Isma1.0 video is based on MPEG-4 Part2, based on SP and ASP, and does not involve H.264, while isma2.0 is Based on H.264;
? Isma2.0 is not compatible with isma1.0, that is, isma1.0's servers and clients cannot be smoothly upgraded to isma2.0. The specific reasons are as follows:
? The encapsulation mode of the video RTP package is not compatible: isma1.0 video RTP packaging follows "rfc3016: RTP payload format for MPEG-4 audio/visual streams ", the isma2.0 video RTP package conforms to the "RTP payload format for H. 264 video "(This RFC has not yet been officially released), added some special restrictions and extensions, for example, it is not allowed to adopt the intertwined mode, or transmit video sequence parameters and frame image parameters through RTP packets;
? The SDP Message format is not compatible: Because the isma1.0 and isma2.0 video RTP packaging methods are different, the SDP message bearer formats and content are different, for example, the definition parameters of the intertwined mode cannot appear in the SDP message. The video sequence parameters and frame image parameters are transmitted through SDP and some special fields are added;
? File Storage Method inconsistent: isma1.0 Based on MPEG-4 part14 (*. MP4), while the isma2.0 file format is based on the MPEG-4 part15 (*. the isma1.0 file format is extended, such as H. the 264 parameter exists in the avcdecoderconfiguration file.
Ii. H.264
At present, H.264 professional encoder is mainly based on ts, and isma2.0, which supports H.264, has just come out and is not yet supported.
3. processing methods and Performance
A) Handling Method
Isma's processing method is: From the encoding end to the decoding end, multiple RTP sessions of audio and video and other data streams must be established. Therefore, when I/O of the streaming server is implemented, the management of multiple inputs and outputs, the management of multiple buffers, and the synchronization between them will greatly increase the processing capability requirements of the streaming server and bring about great algorithm complexity, it also reduces system stability and availability. While ts is reusing multiple audio and video streams and other data streams, only one RTP session needs to be created, so I/O is being performed, buffer Management and audio/video synchronization will be much simpler and easier.
B) port requirements
On Nat and firewall, Isma needs to allocate ports for audio and video RTP separately, which is twice that of TS streams.
C) Performance
From the above processing method, we can see that more RTP sessions need to be managed using the Isma standard, and more I/O and buffer need to be managed, it will greatly consume the CPU performance and memory of the streaming server and STB, thus seriously affecting the system performance. According to the Darwin System and Its experiments, we can only run a few streams on a high-performance machine and there will be a disconnection. If a TS stream is used, several hundred streams of more than 2 m are supported and will not be dropped.
D) Av sync
Isma's AV sync is implemented according to * time stamp in RTP. Therefore, in the same step, you must wait until the RTP of the audio and video arrive before achieving AV sync. The TS Stream does not have this problem because its time information is in a stream. In addition, the AV sync of TS only needs to be implemented at the encoding and decoding end. other links in the middle, such as the stream server, can reduce the algorithm and processing complexity of the streaming server. Isma, on the contrary, not only requires the decoder, but also requires the streaming server to participate in AV sync processing, which consumes resources of the streaming server and increases the algorithm complexity and performance cost, it also reduces the availability and stability of the system.
E) Decoder
Isma has higher requirements on decoder than TS stream. The main task of TS stream is to demultiplexing, that is, demultiplexing needs to analyze the PSI information, then obtain the audio and video PID based on the PSI information, and obtain the video and audio stream through PID filtering, output to the respective buffer. Because ts is a fixed 188-byte packet structure, the position of PID in the packet is fixed and filtering is easy to implement. According to our evaluation, using the software TS Stream de-multiplexing method, on the equator BSP-15 platform, the CPU resources occupied by less than 5%. When Isma is used, due to multiple RTP sessions, multiple buffers are required and managed. Therefore, more memory and CPU resources are used when Isma is used.
4. Support for live broadcasting
A) Channel Switching
If Isma is used for Channel switching on live TV, STB needs to re-obtain the Isma file header from the system. Because a lot of information required for STB decoding is in this file header. Therefore, the system must have a complete set of Isma file headers for generation and management. It also causes a delay in switching the decoding channel.
When live TV performs channel switching, STB also needs to obtain the SDP to obtain some specific parameters required for decoding. In addition, the I frame interval in the traditional Isma stream is longer than 4 seconds, which leads to a long switching time for the STB channel, which cannot meet the requirements of the Telecom standard for 2 seconds.
B) Changes in live video Parameters
During live TV, if the encoder parameter is modified, STB needs to re-establish RTSP session with the encoder or streaming server to obtain the new SDP, then some specific parameters required for decoding can be obtained from SDP. In ts streams, all decoding parameters come along with the bitstream. Therefore, no additional session is required, and the decoder responds faster.
5. trickmode and DRM
A) In Isma, there is no detailed definition of trickmode, especially in RTP. Therefore, the trickmode definitions of different manufacturers are different. As a result, there is no unified standard and the standard is meaningless. If you use the TS stream method, you can define the relevant information of trickmode in its extension. You can define whether the RTP is trickmode or normal playback, and the specific mode of trickmode. At the same time, we can also define a packet loss retransmission mechanism through expansion to ensure the quality of service for users.
B) In Isma, although DRM adopts the AES encryption method, its DRM is not scalable. It does not support multiple DRM methods and encryption standards, and does not support key management. TS just solves this problem. In the RTP extension, you can define the key management method and ing relationship, as well as different DRM methods and standards. This gives the system Extensive compatibility with DRM.
6. Content considerations
A) CP support
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 better adapt to the current situation and requirements of CP.
B) Professional encoder support
Currently, major professional encoders such as tandberg and harmonic all support TS Stream encapsulation formats. Only a few manufacturers support Isma stream formats.
7. Chip support
Currently, all MPEG-4 and H.264 decoding chips support ts. Therefore, selecting ts can provide more options for STB, which helps reduce the cost of STB.
8. Home Network
A) to connect STB to the home network, you must support dlna. In dlna, MPEG-2 and Ts are mandatory standards.
B) All cameras and digital cameras in the home network currently support MPEG-2 ts but not Isma.
C) Currently, all DVR and editing devices in the home network support ts, and Isma is rarely supported.
9. Support for traditional digital TVs
A) Currently, in the radio and television field, DVB uses the TS Stream Encapsulation Format. Therefore, if ts is used, it can be fully compatible with the radio/TV field, especially on STB, which increases the compatibility between IPTV and DVB, this is more conducive to the competition between China Telecom and radio and television.
B) the trend of broadcasting and television is to support H.264 (MPEG-4 AVC) in the future and adopt the TS Stream Encapsulation Format. Therefore, it is helpful for us to smoothly upgrade to H.264. Then, you can directly receive signals from the satellite and directly access the IPTV system without transcoding.
C) Ts is a true open standard, which is conducive to realizing "three-in-one ".
10. media convergence and exchange
The ts format facilitates media exchange and convergence. The ultimate goal of IPTV is to develop into a content exchange network. Apparently, the media file is too large to facilitate content exchange. Each ts package has only 188 bytes, and the format is fixed, facilitating exchange. At the same time, ts is a general standard in the media industry. This facilitates media aggregation and allows us to obtain content from different nodes of the network and aggregate it into a complete content.

Statement 3:

MPEG-2 TS/udp encapsulates media data, including video, audio, and other data, in MPEG-2 ts format, and then carries over UDP and IP protocols, its advantage is that it can carry different encoding standards of media data, and video and audio data transmitted in a stream, easy to achieve video and audio synchronization; disadvantage is that MPEG-2 ts is designed for unidirectional broadcast, the control protocol is not standardized, resulting in poor adaptability to two-way interactive applications such as on-demand, while the fixed 188-byte packet length of MPEG-2 ts makes the transmission efficiency low.

The Isma RTP/udp mode encapsulates video and audio data separately into the RTP format and then carries them on one or more UDP transmission streams, it has good adaptability to two-way interactive applications such as on-demand videos and video communication, and high transmission efficiency. Its disadvantage is that video and audio data are not transmitted in the same stream, and a synchronization mechanism needs to be added.