Reading Notes on Streaming Media Technology getting started and improving

The company is an internet video company. Although I am a developer, I also need to know about video and streaming media because of business problems, so I borrowed the entry and improvement of streaming media technology from the company's library. I have a second version.

Stream technology solution

The so-called stream technology solution is a streaming media application system. Typical systems include: 1. Real Networks; 2. Windows Media; 3. Adobe Flash; 4. Apple QuickTime.

Streaming media servers use special protocols. HTTP is not particularly suitable for streaming media. It has a large number of internal data components and lacks control channels. This is why it cannot stream data forward or backward quickly.

Real System is the first in the system to implement RSTP (Real Time Streaming Protocol) communication. RTSP communication is a kind of physical communication. It is similar in syntax to HTTP/1.1, but there are still many differences. Real system is considered to be the best Streaming Media Transmission System on narrowband networks,

Qiucktime has been widely recognized by the industry by virtue of its outstanding cross-platform features, its small storage space requirements, the independence of technical details, and the high degree of openness of the system. ISO selects the QuickTime file format as the unified digital media storage format for Development MPEG-4 specifications.

Avi, vob, mepg, RM, and MKV are all multimedia containers. They are not a compression format, but a multimedia Encapsulation Format. They are different from the DivX, Xvid, MP3, and Ogg encoding formats. But MKV (matroska) is the most open ).

Stream Media encoding and decoding Technology

Compression encoding based on certain compression algorithms, such as Real Video Based on Wavelet Transform algorithm, Windows Media Based on MPEG-4 compression algorithm.

There are two major international standard series: the mpeg series standard set by ISO/iec jtc; The H.26x video system and the G.7 series Audio Code set by ITU for multimedia communication. The domestic version is AVS with independent intellectual property rights.

MPEG-1 is VCD, MPEG-2 solves the problem of definition, is "HD version of The MPEG-1", MPEG-2 = DVD. However, DVD requires a large capacity, it is difficult to achieve real-time network transmission, so there is a MEPG-4, suitable for low bit rate communication.

In addition, the significance of MPEG4 is the first time in the development history of video encoding to extend the encoding object from the image frame to any shape video object (VO) with practical significance ), the transformation from pixel-based traditional encoding to object-based and content-based modern encoding is realized.

Open source MPEG 4 Encoder: DivX (pseudo open source) and Xvid (true open source ).

The encoding used by HTML 5 is H.264 (MP4). However, due to some patents, h264 is less open than the Ogg format supported by Firefox.

Streaming Media transfer and related Protocols

Regardless of which system, the basic principle is the same: First, we adopt an efficient compression algorithm (reducing the file size while having quality loss ), make a large number of multimedia data files smaller for stream transmission, and then modify the mime representation by assuming the Streaming Media Server, and transmit the stream data through various real-time protocols. Common protocols include RTP, RTCP, RTSP, RSVP, and MMSP.

RTSP Protocol

RTSP uses the HTTP concept wisely so that the structure can be reused. The structure includes the Internet Content Selection platform, text protocol for plaintext reporting, and Web page security mechanism, which can be parsed by standard HTTP or mime parser. You can use UDP or RDP for transmission. When RTSP is used, both the client and server send requests, that is, RSTP can be bidirectional and duplex. When an HTTP request is sent by a client, the server responds. HTTP transmits HTML, while RTP transmits multimedia data.

MMSP Protocol

When the MSS protocol is used to link to the publishing point, the MMS protocol automatically finds the optimal transmission path of streaming media in the following order:

(1) UDP (User Datagram Protocol)

(2) TCP (Transmission Control Protocol)

(3) HTTP (Hypertext Transfer Protocol)

UDP is a connectionless transport layer protocol, which is an ideal protocol for real-time media because it does not guarantee transmission. Although this seems to be a disadvantage rather than an advantage, it is a very suitable feature for streaming media. Streaming media data is different from file and email data: files, emails, and other data must be transmitted as a whole regardless of the transmission time. However, the value of streaming media data is limited by time, if a video frame is lost and cannot be reached within the correct time frame, there is no value. Once again, it is said that this data is a waste of bandwidth. It is possible to specify UDP as the transmission protocol only. To do this, you can use the following methods:

Mmsu: // servername/filename. ASF

Here mmsu indicates that the MMS protocol and UDP protocol are used for data transmission.

The disadvantage of UDP is that it cannot pass through the company's firewall. Or you need your network administrator to open it. If the mmsu connection fails, and the server tries to use mmst, it uses the MMS protocol to combine TCP. TCP is the mainstream Internet transmission protocol. Its disadvantage is that it will try to re-transmit data and may not be able to pass through the company's firewall. Specify the syntax to use TCP as the transport protocol only:

Mmst: // servername/filename. ASF

The last option is HTTP. Although HTTP is an application-layer protocol rather than a transport-layer protocol, and it is specially designed for streaming media, it can use the firewall, anyone who can browse the Web can accept stream files through the HTTP protocol. Specify the syntax to use TCP as the transport protocol only:

Http: // servername/filename. ASF

P2P protocol

Peer-to-Peer P2P is generated to solve the problem of increasing server load in the C/S mode. P2P is mainly applied to distributed networks, where distributed networks can be divided into structured and non-structured networks.

In unstructured P2P 1, a peering machine traverses the entire network through a connection with an adjacent peer machine (this search method is called a flood flooding search ). Each peer has similar functions and does not have a dedicated server. However, the peer level must rely on the distributed network where they are located to find files and locate resources on other peers.

In Structured P2P, a network node is assigned a unique node identifier in a certain way. All operations related to searching and routing are based on DHT (Distributed Hash table) the distributed discovery and routing algorithms are implemented at the overlay layer. In essence, the redirection mechanism is introduced when searching for files and other clients. The core is DHT.

P2P live broadcast

The P2P live broadcasting room is the best embodiment of P2P value. Users are watching the same program and the content is similar. Online users can be almost unlimited.

The mesh multicast mode has been hailed as a milestone in live streaming media. Application Examples: PPLIVE and PPStream (Unstructured Network Protocol)

VOD

It is expected that the development of large-scale distributed digital copyright protection (DRM) and underlying encoding technology will pave the way for the implementation of P2P VoD Systems.

P2P Network Structure

Two main categories: tree-based he data-driven randomization coverage network structure.

BT's typical unstructured network protocols include Gnutella and KaZaA (but there is a "super node", similar solutions include Skype)

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