Bitrate is the number of bits that are transmitted or processed over time. The Bitrate is expressed in the unit bit per second (bit/s), often in conjunction with a prefix such as kilo (1 kbit/s = 1,000 bit/s), mega (1 Mbit/s = 1,000 kbit/s), giga (1 Gbit/s = 1,000 Mbit/s) or tera (1 Tbit/s = 1,000 Gbit/s).
Constant Bitrate vs. Variable Bitrate
The bitrate for audio or video compression can be either constant (CBR) or variable (VBR). Constant bitrate keeps the bitrate fixed independent of the underlying signal while variable bitrate may vary the bitrate depending on the complexity of the signal.
Factors that effect Bitrate for Video Streaming
The bitrate observed during video streaming depends on several factors:
- Image resolution (HD, Full HD, WQHD, UHD / 4K)
- Frame rate
- Video Compression
- Complexity of the video, caused by activity or change in the camera scene
How does Video Compression effect Bitrate?
Video compression reduces the bitrate during video streaming. Common video compression technologies for security cameras include: MJPEG, h.264 and h.265. MJPEG has the highest bitrate because it only compresses individual frames. In comparison to MJPEG, h.264 and h.265 also compress information in between frames which reduces bandwidth significantly. While h.264 is still used in the majority of products, h.265 is the most advanced standard and reduces bandwidth significantly when compared to h.264 by leveraging coding tree units (CTUs). CTUs divide the image into separate blocks where block size is adjusted to the complexity of the image region.