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The NLSS Decoder and Multi-Stream Views

Last Updated: Jan 30, 2017 08:55AM PST
Article: 4.00-kdb-0003 

 The NLSS Decoder is a device built to take video streams from the network and display them on a digital monitor.  There are a number of limits and caveats as to what it is capable of displaying and this article aims to help clarify  some of these limitations.

The NLSS Decoder has a number of "Views" that it is capable of displaying.  Each "View" is made up of a number of "Panes".  The Decoder can place either a video stream or uploaded media in each pane.  Views include either 1x1, 2x2, 3x3, 4x4, 1x4, or 2x4.

The decoder is also capable of running 2 monitors simultaneously, but again, the number of simultaneous panes being displayed limits what the decoder is capable of doing.  The best way to think about the decoder when running multiple monitors is to think of a dual monitor desktop computer running in "stretched display" mode.  We will cover more on this later in the article.

Hardware Affected: DC400, DC400-2
Software Affected: ALL 
 Resolution and a display monitor 

With the advent of High Definition TV’s came a standard in video resolution that most monitors and TV’s adhere to.  By far and away the most common video resolution is 1920x1080. What this means is that the monitor has 1920 horizontal lines of resolution and 1080 lines of vertical resolution (more on this here).

IP security and surveillance cameras have mostly followed with this paradigm.  The most common resolution an ip camera puts out it 1920x1080 lines of resolution.  The most common exception is a “multimegapixelâ€� camera that is 5 or even 10 “Megapixelsâ€� in resolution.

 Resolution and what the decoder can display 

High Definition camera that display 1920 x 1080 lines work very well with a NLSS Decoder that is hooked to a 1920 x 1080 line monitor.  This is a 1 to 1 correlation and the decoder can spend its resources simply decoding the image and rendering it on the monitor.  This get very complicated, however, when there are multiple panes to display, as is the case with, say, a 2x2 view.  Consider that for a 2x2 view, the decoder must not only decode and render 4 streams, but it also has to scale each of the 1920x1080 streams down to only 960 x 540 lines of resolution.  As the task of decoding more and more streams is put on the decoder (especially with a 3x3 or a 4x4 view), it is understandable that the decoder simply cannot keep up with the load and the total amount of work needs to reduced.

The simplest way of reducing this burden is the reduce the resolution and framerate of each stream such that the decoder can keep up.  The best way of doing so is to simply ask the camera for a smaller frame rate and resolution.  Commonly, many cameras are capable of providing multiple streams.  For example, one stream may be used by recording software such that one high resolution / high quality image is kept for forensic purposes while an additional lower framerate and resolution image is used to send to the decoder so it can render multiple views.

For reference, please see the below diagrams which show the resolution of each pane of video within a 2x2, 3x3, or 4x4 layout.  Also, please see the decoder datasheet (here) for a full description of how many images the decoder is displaying at what frame rate and resolution.

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