April 2012 Archives

Bandwidth

Brian Karas
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How much bandwidth do I need?
Can I use a DSL connection?
How much data do the cameras send?
Will this work with a 3G card?
How many cameras will a cable modem support?

These are all questions we hear frequently.  When dealing with IP devices - cameras, encoders, printers, whatever, it's understood that device is going to use some amount of network resources to communicate.  Cameras in particular have a reputation of being "bandwidth hogs".

Figuring out how much bandwidth is needed is not a complex calculation, but there is also no "one size fits all" answer.

VideoIQ devices send data across the network in three primary scenarios:
1) When an alarm event occurs - the alarm clip is sent to any PC(s) logged into that unit and/or to any FTP servers configured to receive push events on the camera

2) When a user is watching a live video stream from the device

3) When the Archive process is backing up recorded video.

A couple of terms that you often hear in relation to bandwidth calculation are "VBR" and "CBR".  

VBR is "Variable Bit Rate", meaning that the bandwidth used may change from one moment to the next.  Sometimes by a small amount, sometimes by a large amount.  VBR is common when you want to specify a fixed quality level and then let the camera use as much bandwidth as it needs to meet that target.  This sounds good on the surface, and there are good applications for VBR, but it also frequently results in cameras consuming massive amounts at unexpected times, and not always with obvious quality.  Changing resolution and/or framerate will tend to have a direct impact on the bandwidth used, since higher resolutions or more frames per second will require more data.

CBR is "Constant Bit Rate", the user defines the target bitrate for a given video stream configuration, and the streaming software compresses it using the selected format (H.264, MJPG, etc.) to fit in the allocated bandwidth.  Changing resolution settings for a CBR configuration will NOT impact the bandwidth used, since the bandwidth is configured to a fixed setting.  Image quality is what gets impacted.  With a CBR system, we can specify a target bitrate of say 2Mbps, which could produce a really nice image for a 720p image stream at 2.5fps, but would not be very good for a 1080p stream at 30fps.  Both image streams would use the same bandwidth (2Mbps), but the lower resolution stream would likely LOOK better, because it wouldn't be as heavily compressed as the 1080p stream. The benefit of CBR is that you get very predictable bandwidth (and storage) calculations, but need to understand what settings may or may not be optimal.

VideoIQ uses CBR bandwidth management on all current devices.  Bitrate settings for individual streams are configured in the Storage and Compression settings of the Camera Settings (accessed by right-clicking the camera icon in the tree.

BandwidthSettings.pngChanging resolution or framerate will NOT affect bandwidth or storage times.  However, selecting a high resolution and framerate in conjunction with a low bandwidth speed will result in image compression that may product noticeable degradation.  For 1080p streams it is recommended to choose a bitrate setting of 4.5Mbps or higher. 

There may be aspects of your network connectivity, especially over wireless networks, that prevent you from viewing a live stream above a few hundred kbps.  A setting of 500Kbps for the non-alarm stream is usually sufficient to produce a decent quality 960x540 pixel image at 2.5 or 5 fps.  Because of the way the VideoIQ devices operate, you can always choose to record the higher resolution stream, even if it won't be viewed live.  The Export feature makes it easy to copy out hi-res video in selected intervals.  Because this is a file transfer instead of a live stream at that point, you can export the videos even over a low speed connection, it just may take 3-10x as long as the export duration to transfer the video (eg: a 30 minute segment of video could take 2-5 hours to transfer over a low speed connection).




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This page is an archive of entries from April 2012 listed from newest to oldest.

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