Model 2416S-DVR

Mpeg Video Server
Sensoray Vendor:
Sensoray
  • Details
* NA
Discontinued product. Available on special order
  • Hardware compression, decompression of PAL, NTSC into MPEG2 or MPEG1
  • Text caption buffer
  • Internal web server and dynamic web pages
  • Onboard removable compact flash
Description

Model 2416S-DVR is an Ethernet based digital video recorder. It converts analog video into digital data, compresses it into MPEG formats and then transmits it over an Ethernet using the UDP or RTP protocol or stores it locally on a removable compact flash drive. It is made from Sensorays 516 MPEG-2 frame grabber, 301-6 CPU and 207 power supply. Since the 2416S-DVR is bi-directional, it can accept an Ethernet stream from another 2416 and convert the encoded digital video into composite video outputs.

Video Storage

An onboard removable compact flash opening allows for the storage of recorded video clips. The video clips can be accessed remotely by ftp, played back locally on the device, or taken with you by removing the compact flash card and replacing it with another. A mechanical lever holds the card in place for environments with high vibration.

Audio Capture

Model 2416S-DVR has a stereo audio input channels that is synchronized to the MPEG data.

Decoding Latency

Although it is possible to use the 2416S-DVR hardware to decode MPEG data, this process does not have low latency compared to Sensorays Display & Control software. 2416S-DVR hardware latency is 5 seconds, while our software players latency is less than one second.

Display and Control Software

Sensorays real-time Display and Control Software decodes and displays up to fifteen MPEG1 and/or MPEG2 streams with a low latency of 1/2 to one second. Thumbnail images from remote video servers may be positioned over a background such as a map or building plan. Multiple server images may be selected for expansion to full size and full frame rate.

Ethernet Protocols

The UDP format (user datagram protocol) offers the fastest data rates and minimum CPU usage at the expense of minimal error checking. The 2416-4 can uni-cast four MPEG2 data streams at full frame rates when using this protocol.

A disadvantage of the UDP format is that it cannot be played using popular stream players such as QuickTime. However, the latency i.e., the time delay between recording and displaying, while using these players, can be several seconds.

The RTP format (real time protocol) trades off CPU and memory usage for error correction and compatibility with QuickTime and Real Player. Sensoray sells a multi-stream, low-latency software RTP player for Windows 2000 and XP. The latency of Sensorays software player can be as low as one half second when processed on a 2 GHz, Pentium-4 system. A disadvantage of RTP is that it uses twenty-five percent of the 2416’s CPU time, while UDP uses less than five percent. Hence, the 2416 can only support two RTP streams.

Bit Rates and Bandwidth

The data rates discussed below refer to the bit rate from the MPEG frame grabber used by the 2416S-DVR. The rates do not refer to Ethernet bit rates, which are fixed at 10 Mbits/sec or 100 Mbits/sec. The 2416S-DVRs programmable bit rate allows trading image quality for bandwidth.

Higher bit rates from our MPEG frame grabber give better quality images than lower rates. Full-size interlaced images of 30 frames/sec will start to show distortions below 1 Mbits/sec, however, image quality improves only slightly above this rate.

When low bit rates are selected e.g., 100 Kbits/sec, the amount of distortion depends on the amount of motion in the scene. A chess game will have less distortion than a soccer game.

A variable bit rate may also be selected. This mode tries to maintain good image quality by varying the frame grabber bit rate according to the amount of motion in the scene.

It is also possible to decrease the bandwidth by decreasing the image size. Selecting CIF size images of 320 x 240 pixels will reduce the required bit rate by four compared to 640 x 480 pixel images that occur at the same frame rate.

If there is not much motion in a scene, a lower frame rate may be selected to reduce the frame grabbers bit rate. Lower frame rates will show motion artifacts from fast-moving objects. Even though such as stream can be recorded at a lower frame rate, most MPEG viewing programs will play the stream at 30 frames/sec for NTSC and 25 frames/sec for PAL. The stream will be playing in a fast-forward mode. For example, a 15-frame/sec recording will be displayed at twice the normal frame rate.

Embedded Linux

The board set is supplied with specially configured Linux for high reliability and fast response. After power is applied, the software is automatically loaded to RAM from flash memory. The 2416S-DVR will then stream MPEG data to the Ethernet port or save it locally to the compact flash drive.
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