Posts Tagged ‘ dual stream’

CCTV How To Get A Good Sub Stream

Written By:
Friday, December 18th, 2009

One of the advantages of having today’s DVRs vs the older time lapse VCRs for recording your security camera footage is the ability to connect the DVR to your network. By doing so, you have just opened up a whole new world of possibilities. Many of todays modern DVRs have a built in web server that would allow you to view your cameras remotely from any internet browser, anywhere in the world that has an internet connection. Some also have sophisticated monitoring software that allows you to monitor your security cameras from multiple locations at the same time. For example, you may have a surveillance system installed in your business, and in your home, and with monitoring software, you could connect to both at the same time. All of this great technology comes at a price. That price is called bandwidth. Gone are the days of the old AOL dial up service that provided 33kbps – 56kbps bandwidth. Today’s typical needs are now in the 3mbps -5mbps and often higher. The most demanding bandwidth hogs on the internet that I can think of are videos.  You may think of videos as what you watch on but a huge amount of bandwidth is used by security camera videos that are streamed from millions of security cameras over the internet every minute of every day. As the quality of today’s security cameras increase, the size of the video file being streamed also increases. A high resolution video stream from a single security camera may use up 500kbps or more bandwidth, so it is not hard to imagine a 16 camera surveillance system requiring upwards of 8mbps to stream high quality video over the internet.

Most people don’t realize, but they are being misled by their internet service provider into believing they have greater bandwidth than they really do. DSL for example, often advertises 6mbps or more bandwidth, but what they don’t tell you is that is the “down” bandwidth which is used for downloading. however, if you have a security camera system in your business and you need to stream that video to you at home, the DVR is actually going to use the “up” bandwidth, not the down bandwidth. With DSL, the up bandwidth can var between 256kbps and 750kbps. So, even though you purchased 6mbps bandwidth, you will only see 6mbps on the downstream and maybe 750kbps on the upstream. So, how do today’s security professionals handle the “up” bandwidth restrictions?

In most cases, they will need to lower the quality of your video recording. They do this by lowering the frame rate (frames per second the video records in), lowering the resolution, lowering the bit rate, or lowering the quality of the recording. This would allow for a more efficient use of the bandwidth. If you lower the quality settings enough, I have seen a single camera stream compressed to below 30kbps. the result is poor image quality, but in exchange, the ability to squeeze a 16 camera video stream out. There is another option, but only with a DVR that has the ability to put out a sub stream. A sub stream is just a secondary video stream that is set at a lower quality setting. Basically, this means you can keep your recorded video at the highest available quality settings. Maximize the frame rate, bit rate, resolution and quality for recording, but on the sub stream you can lower it to reduce the amount of needed bandwidth. The end result is high quality recordings and the ability to stream 16 cameras through a narrow bandwidth. In essence, this is the best of both worlds.

sub streams are not common place yet, but some of the higher end DVRs do offer this feature. If you plan on networking you DVR for remote access, I highly recommend you consider a DVR that has a sub stream.


What is a Substream?

Written By:
Tuesday, September 15th, 2009

Some of the newer DVRs on the market offer a feature called either a substream or a dual stream. A sub stream is used for viewing your DVR over the LAN or WAN when the resolution or frame rate of the recorded video is too high for the available bandwidth. For example, if your DVR was recording at 4CIF (or D1) resolution which is 704×480 in realtime (30fps), that would provide you with some exceptional recorded footage that would be both 4 times larger than the average CIF (360×240) recording and in realtime. Unfortunately, in most cases you would not be able to remotely view the video with fluid motion over the internet because there would not be enough available up bandwidth coming from the DVR location. In this case you would benefit from a sub stream that would be set at a lower resolution like CIF (360×240). This would allow you to have a high quality recording, but still be able to view fluid video over the internet.