Key concepts
Page 10
FortiRecorder 2.4.2 Administration Guide
General performance factors
The following factors affect the input side of performance:
• Total number of video streams from the cameras (i.e. not just the number of cameras)
• The video recording types (motion only or continuous) per camera
• The video stream parameters per camera – i.e. video compression (constant or variable bit
rate mode), image quality level, complexity of the scene, video resolution and frame rate per
second.
The following factors affect the output side of performance:
• Number of administrator/operator/viewer sessions
• Peak number of simultaneous administrator/operator/viewer live views
• The video stream parameters per camera live view – i.e. video compression (constant or
variable bit rate mode), image quality level, complexity of the scene, video resolution and
frame rate per second.
Variable versus constant bit rate
The variable bit rate mode means the bandwidth used by the camera will vary according to what
the camera is seeing and the video profile settings. The video profile settings for the variable bit
rate mode are resolution, frame rate and image quality. High resolution creates more data than
medium or low resolution (see following sections for more detail). The degree of motion present
in a video stream also affects the amount of data created.
The constant bit rate mode means the bandwidth used by the camera will stay relatively
constant regardless of what the camera is seeing. The constant bit rate mode is therefore more
predictable in deployments where bandwidth and/or storage capacities are important
considerations. The video profile settings for the constant bit rate mode are resolution, frame
rate and bit rate. The bandwidth used by the stream is dictated by the bit rate setting.
In general, using the variable bit rate mode results in relatively consistent video quality but
fluctuating bandwidth and using the constant bit rate mode results in varying video quality but
predictable bandwidth. Choosing a high bandwidth constant bit rate mode avoids the video
quality drop e.g. during high motion, but may use some unnecessary bandwidth during times of
no activity.
However, in most cases the difference in video quality between the variable and constant bit
modes is negligible (assuming the same resolution and frame rates) and the constant bit rate
mode produces more reliable output from the cameras.
Bandwidth per camera or live view
Variable bit rate
Depending on resolution, frame rate and video quality a camera using H.264 compression may
generate the following bit rates:
• 352 x 240 @ 30 FPS, high quality = 0.4 Mbps
• 720 x 576 @ 30 FPS, high quality = 1 Mbps
• 1280 x 720 @ 30 FPS, high quality = 2 Mbps
• 1920 x 1080 @ 30 FPS, high quality = 4 Mbps
• 1920 x 1080 @ 30 FPS, medium quality = 2.8 Mbps
• 1920 x 1080 @ 30 FPS, low quality = 2 Mbps
• 1920 x 1080 @ 10 FPS, high quality = 2.4 Mbps
• 1920 x 1080 @ 10 FPS, low quality = 1.2 Mbps
