Currently on the market for hard disk video recorder products many varieties. How to select a most suitable hard disk video recorder, for many users is a difficult problem, especially for beginners, is unable to start, choose the hard disk video recorder, region free dvd should focus on the hard disk video image compression method, image quality, real-time, network performance, stability, after sale service and price.

 

Computer hard disk video recorder ( PC-BASEDDVR ) is based upon the industrial control computer hardware, operating system based on WINDOWS software, equipped with audio and video compression card, with the help of professional compression algorithm and PC hardware and software capacity towards monitoring system video and audio signal recording and playback apparatus. Industrial control DVR core equipment is the audio and video compression card. Compression method, image compression technology is the quality of hard disk video recorder core, Zone Free DVD dab6d28ck the choice of compression method is the key. Here it is necessary to take into account the image quality, and also take into account the image storage and transmission speed. At present, appear on the market the hard disk video card compression methods are mainly M-JPE, wavelet algorithm, MPEG-1, H263, MPEG-4, H.264 etc.. M-JPEG ( 1 ) we can think of is the first generation of monitoring compression standard ( 1995 ) begins to popularize a considerable part of domestic and foreign network cameras and video servers are using MJPEG compression technology, such as SONY launched AXIS2130PTZ SNCZ2OP network camera, network camera. MJPEG means MotionJPEG, dynamic JPEG, according to the 25 frame / sec ( PAL ) in the rate of use of JPEG algorithm for compressed video signal, a dynamic video compression. Is a JPEG prepared by the group of experts, the image format of each frame is compressed, usually can reach 6:1 compression rate. As each frame is independent of the image. MJPEG image flow unit is a frame of a frame JPEG picture. Because each frame can be arbitrarily access, so MJPEG is often used for video editing system. Dynamic JPEG can produce high quality, full screen, full motion video, however, it needs to rely on additional hardware. Also, because MJPEG is not a standardized format, each manufacturer has their own version of the MJPEG, both the file cannot be mutual recognition. So MJPEG has begun to gradually fade out video processing field.

 

The advantage of MJPEG is that quality is relatively clear, disadvantages of compression rate is low, the huge bandwidth. General single occupied bandwidth 2M～ 3M. In dealing with a huge deal will lead to video workstation was unable to complete a plethora of video data, will cause great cause network congestion network data flow. Due to the compression of relatively small, so the storage server data storage will become a problem. In the 100MB network can not real time transmission route 16, 852printing per hour of video data volume more than 500MB. This problem is the biggest obstacle of network equipment. And Motion-JPEG compression technology does not support audio and video synchronization, so even if some enterprises developed audio components, but also frequently appears sound and video are not synchronized question. Taiwan and South Korea, many of the early products using this compression method, but it has gradually eliminated from the market. 2) WaveletTransform (first half ) ( 1997 start ) wavelet transform also belong to the intraframe compression technology, due to the compression method to remove the high-frequency components of the images, retaining only the single frame image signal, especially suitable for screen changes on frequent occasions, and the compression ratio is also obtained certain enhancement, so are some network the camera used, for example, BOSCH launched NetCam-4 series of digital network camera. But the total amount of compressed data is not much changed, and the image quality is obviously decreased. 3) H.263 (second generation ) ( 1998 start ) H.263 is a mature standard, H.263 video coding standard is designed for high quality image compression the designed low bit-rate image compression standard. H.263 based video coding common encoding method, encoding process is divided into coding and interframe coding two parts. In the frame by using the improved DCT transform and quantization, in between the frames using 1/2 pixel motion vector prediction compensation technology, so that more accurate quantification of motion compensation, after the application of improved variable length coding table ( VLC ) quantified data entropy coding, to get the final coding coefficient.