Bandwidth and Storage Space Calulations

Network video products utilize the bandwidth and storage space depending on its configuration. This depends on the following:- Number of cameras- If the recording will be continuous or event-based- Number of hours per day that the camera is recording- Frames per second- Image Resolution- Video compression type : Motion JPEG , MPEG - 4, H.264- Landscape : the complexity of the image ( for example, gray wall or a forest ) , lighting conditions  and the amount of movement ( office environment or train stations crowded)- How long should store dataBandwidth requirementsIn a surveillance system that involves small chambers 8 to 10 , a switch core network 100 - megabit (Mbit ) can be used without having to consider bandwidth limitations . Most companies can implement a monitoring systemsystem of this size using your existing network. By applying 10 or more cameras , the network load can be calculated with a few golden rules : A camera that is configured to provide high quality images at high frame rates used approx . From 2-3 Mbit / s of network bandwidth available.- With more than 12-15 cameras , consider the use of a switch with a gigabit backbone .
If you use a gigabit switch support, the server running the video management software must have a gigabit network adapter installed.The technologies that allow management of bandwidth consumption include the use of VLANs on a switched network , Quality of Service and event-based recordings .Calculating storage needsAs mentioned above , the type of video compression used is one of the factors affecting storage requirements . The H.264 compression format is by far the technique more efficient video compression available today . Without compromising the image quality , an H.264 encoder can reduce the size of a digital video file by more than 80% compared with the Motion JPEG format and as much as 50% more than the standard MPEG - 4 . This means much less bandwidth and network storage space required for a H.264 video file . Sample calculations storage for three compression formats are provided in the following tables. Due to a number of variables that affect average levels of bit rate, the calculations are not so clear for H.264 and MPEG - 4. With Motion JPEG , there is a clear formula for Motion JPEG is a separate file for each image. The storage requirements for Motion JPEG recordings vary depending on the rate , resolution and compression level frame.Approx. bit rate / 8 (bits in a byte ) x 3600 = KB per hour / 1,000 = MB per hourMB per hour x hours of operation per day / 1000 = GB per dayGB per day x period requested storage = storage requirementMPEG - 4 calculationApprox. bit rate / 8 (bits in a byte ) x 3600 = KB per hour / 1,000 = MB per hourMB per hour x hours of operation per day / 1000 = GB per dayGB per day x period requested storage = storage requirementNote: The formula does not take into account the amount of movement , which is an important factor which can influence the storage size requiredCalculation Motion JPEGImage size x frames per second x 3600s = kilobyte ( KB ) by hour/1000 = Megabyte ( MB ) per hourMB per hour x hours of operation per day / 1000 = Gigabyte (GB ) per dayGB per day x period requested storage = storage requirementIn order to achieve efficient video transmission , it is important to assess their bandwidth needs before establishing IP surveillance system .Bandwidth requirements vary with the following factors .

• Resolution: the higher the resolution , it requires more bandwidth
• The complexity of the scene : the more complicates the scene requires the most bandwidth
• Compression Type: the lower compression ratio , it requires more bandwidth
• Image quality: Superior image quality , requires more bandwidth.
• Frame rate: the higher frame rate , it requires more bandwidth.

The variable bit rates steadyWith MPEG - 4 and H.264 , users can allow an encoded video stream to have a variable or constant bit rate . The optimal choice depends on the application and network infrastructure . With VBR ( variable bit rate ) , a predefined level of image quality can be maintained regardless of the movement or the lack of it in a scene. This means that the use of bandwidth is increased when there is a lot of activity in a scene and decrease when no motion . This is often desirable in video surveillance applications where there is a need for high quality , particularly if there is movement in a scene. Since the bit rate can vary, even when defined average bit rate target , the network infrastructure ( available bandwidth ) must be able to accommodate high yields. With limited bandwidth available , the recommended way is usually CBR ( constant bit rate ) as this mode generates a constant bit rate that can be preset by a user. CBR is the disadvantage that when , for example, increased activity in a scene that is in a bit rate that is higher than the target rate, the restriction to keep the wires from constant bitrate to a lower image quality and frame rate . Most network video products allows the user to prioritize the quality or frame rate if the rate rises above the target bit rate .3 Methods different video compression include:- 1PASS - VBR- 1PASS -CBR- 2pass -CBR

With 1PASS - VBR , you can not know the size of the resulting file , because the bit rate is distributed according to the amount of movement , but it is possible to encode the video quality . With 1PASS - CBR , you can encode the video into a set size since it applies the same amount of bit rate, regardless of the type of video . 2pass - CBR is the combination of the two methods. In the initial coding checks the status of the video and its secondary encoding bit rate amount is distributed according to the state of the video to provide a good quality fixed size for the output file .The advantages of VBR are that it produces a better space value in comparison to a CBR file of the same data . The available bits are used more flexibly to encode audio data or video with greater accuracy with a smaller number of bits used in passages or made more difficult bits used to encode passages .The disadvantages are that it may take longer to encode , because the process is more complex , and that some hardware may not be compatible with VBR files .