The frame rate of the USB camera module is closely related to the bandwidth. The higher the frame rate, the greater the required bandwidth. The following is a specific analysis:
The basic relationship between frame rate and bandwidth
Frame rate refers to the number of images displayed per second, measured in fps (frames per second). Bandwidth refers to the amount of data transmitted within a unit of time (1 second), usually expressed by the transmission rate, with the unit being bps (bits per second). Among the camera parameters, frame rate and bandwidth are interrelated. The higher the frame rate, the more image data needs to be transmitted per second, and thus the greater the required bandwidth.
Bandwidth requirements at different resolutions and frame rates
720P resolution: Taking a camera with a resolution of 720P (1280×720) and a frame rate of 30fps as an example, the data volume of each frame of image is relatively small, but 30 frames of images need to be transmitted per second, so a certain bandwidth is still required. Generally speaking, for a 720P resolution camera at a frame rate of 30fps, the bit rate of each camera stream may be around 2Mbps.
1080P resolution: For cameras with a resolution of 1080P (1920×1080), the amount of data per frame of the image is greater. At a frame rate of 30fps, the bit rate of each camera may reach 4Mbps (using H.264 encoding) or even higher (for example, it may be around 2Mbps when using H.265 encoding, but in actual transmission, it may vary due to factors such as encoding efficiency and image content). If the frame rate is increased to 60fps, the required bandwidth will double.
Higher resolution: For cameras with higher resolutions such as 4K (3840×2160), the amount of data per frame of image is extremely large, and thus the required bandwidth is also higher. At a frame rate of 30fps, the bitrate of a 4K camera may reach 13Mbps to 38Mbps (after compression using H.265 encoding).
Bandwidth limitation and frame rate adjustment
USB interface bandwidth: The bandwidth of the USB interface is limited. Για παράδειγμα, the theoretical transmission speed of USB 2.0 is 480Mbps (the actual transmission speed usually does not exceed 30MB/s, that is, 240Mbps), while the theoretical transmission speed of USB 3.0 can reach 5Gbps (the actual transmission speed is usually between 400MB/s and 600MB/s). When the bandwidth required for the frame rate and resolution of the camera exceeds that of the USB interface, it may cause problems such as incoherent images and lag.
Frame rate adjustment: To achieve smooth video transmission within a limited bandwidth, the amount of image data that needs to be transmitted per second can be reduced by lowering the frame rate. For instance, reducing the frame rate from 60fps to 30fps can halve the required bandwidth.