In this design, the data exists in the form of stream data throughout the system. The Linux kernel provides a standard programming interface for streaming data. This interface provides a full double for data from external devices to the user process via the kernel. Work channel.
In this channel, the data processing module is dynamically loaded by the user as an optional middleware. The video compression module designed above is such a middleware.
2 ASF streaming file formatThis system is mainly used for real-time video applications, so the system needs to provide support for streaming file format, so that the receiver can watch the real-time transmitted video by using the standard streaming video playing software, such as MMedia Player. It is adopted in this system. Open ASF stream format. The compressed video data needs to be ASF encoded before transmission. The basic organizational unit of ASF file is ASF object, and each object consists of three fields: object identifier field, object size field and object. Data field. The high-level logical structure of an ASF file also contains three parts: a header object, a data object, and an index object. Among them, the header object contains a lot of global information, the data object contains all the data to be played, and the header object must be received and interpreted by the receiver between the data objects.
The streaming video protocol is designed and standardized for communication between the client and the video server. According to their functions, the protocols related to streaming video on the network fall into three categories.
* Network layer protocol: The network layer protocol provides basic network service support. IP is the network protocol used by streaming video on the network.
* Transmission Protocol: The transport protocol provides end-to-end network transport for streaming services. TCP, UDP, RTP, and RTCP are the transport protocols used by streaming video over the network.
* Voice Control Protocol: The voice control protocol defines messages and procedures. RTSP is a voice channel control protocol.
The protocol stack designed for streaming video is shown in Figure 4. On the sender's data side, the compressed and ASF encoded video data is read and packed on the RTP/RTCP/RTSP layer to provide timing and synchronization information as well as the sequence number of the packet. These packed RTP data streams are then sent to the UDP/TCP layer and the IP layer, and the resulting IP packets are transmitted over the network. On the receiving side, it is processed in the opposite direction. On the control plane, the RTCP packet and the RTSP packet are multiplexed on the UDP/TCP layer and sent to the IP layer for transmission over the network.
summaryThis paper proposes a design scheme based on Intel PXA255 embedded microprocessor and embedded Linux network camera. The system adopts advanced MPEG-4 coding standard and obtains a high compression ratio. After testing, the CIF (352 & TImes; 288, 30FPs) format video has better performance in the bandwidth of 50Kbps ~ 100Kbps. It satisfies the requirements of network video conferencing and video surveillance in the current broadband environment, and its application is very extensive.
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