VBR/CBR/ABR/CABR/Per title/Constant QP/CRF

VBR/CBR/ABR/CABR/Per title/Constant QP/CRF are rate control modes that affect the bitrate of the output video stream.

• CBR ( Constant bitrate) - encoding of a video sequence with a constant bitrate, regardless of its complexity. The output stream has a specified bitrate, this is useful when broadcasting to the network, but the encoding is less efficient. As the complexity of the content increases, the image quality may deteriorate due to a lack of buffer. Or vice versa, when reducing the complexity of the content, the encoder can output an excessive stream size to ensure a given bitrate level.
• VBR (Variable bitrate) - the bitrate can change automatically in a given range, depending on the complexity of encoding the content, and is selected by the encoder. A very effective method of encoding, but when broadcasting to the network, the bandwidth is not used effectively because of the changing bitrate.
• ABR (Average Bitrate) - the mode is similar to VBR, in which the encoder keeps the average bitrate value near a given level.
• CABR (Content Adaptive BitRate) is an encoding mode designed to increase the quality while reducing the bitrate by adapting to the content of the input stream.
• Per Title is an adaptive encoding mode, in which the best bitrate/quality ratio is selected, which is evaluated using a large amount of stream transcoding.
• Constant QP (Constant Quantization Parameter) - rate control mode, in which the quantization parameters are set constant. Quantization parameters are used to control the level of compression of macroblocks of a frame by throwing out a certain amount of information from it.
• CRF (Constant Rate Factor) - encoding mode with constant quality. Unlike Constant QP, it encodes frames with different quantization parameters to achieve the same quality. CRF changes QP depending on the motion, with a large motion in the frame, QP can be increased, with a smooth motion, QP can be lowered.