ABR – Average Bit Rate
Average Bit Rate (ABR) is the average amount of data transferred per unit of time, usually measured per second, usually for digital video or music.
For example, an MP3 file with an average bit rate of 128 kbps transfers an average of 128,000 bits per second. It can have higher and lower bitrate portions, and the average bitrate for a particular time period is obtained by dividing the number of bits used during the time period by the number of seconds in the time period. Bitrate is unreliable as an independent measure of audio / video quality because more efficient compression methods use lower bit rates to encode material of similar quality. Average bitrate can also refer to a form of variable bit rate (VBR) encoding in which the encoder will try to reach the average bitrate or target file size, allowing the bitrate to vary between different parts of the audio or video. Since it is a kind of variable bit rate, it allows more complex parts of the material to use more bits and less complex areas to use fewer bits. However, the bit rate will not change as much as with variable bit rate encoding. At a given bit rate, VBR is usually higher quality than ABR, which is higher quality than CBR (constant bit rate). ABR encoding is desirable for users who want the general benefits of VBR (optimal frame-to-frame rate) encoding, but with a relatively predictable file size. Accurate ABR encoding generally requires two-pass encoding, as in the first pass, the encoder has no way of knowing which parts of the audio or video require the highest bit rate to encode.
VBR Variable bit rate
Average Bit Rate (ABR) is the average amount of data transferred per unit of time, usually measured per second, usually for digital video or music. For example, an MP3 file with an average bit rate of 128 kbps transfers an average of 128,000 bits per second. It can have higher and lower bitrate portions, and the average bitrate for a particular time period is obtained by dividing the number of bits used during the time period by the number of seconds in the time period. Bitrate is unreliable as an independent measure of audio / video quality because more efficient compression methods use lower bit rates to encode material of similar quality. Average bitrate can also refer to a form of variable bit rate (VBR) encoding in which the encoder will try to reach the average bitrate or target file size, allowing the bitrate to vary between different parts of the audio or video. Since it is a kind of variable bit rate, it allows more complex parts of the material to use more bits and less complex areas to use fewer bits. However, the bit rate will not change as much as with variable bit rate encoding. At a given bit rate, VBR is usually higher quality than ABR, which is higher quality than CBR (constant bit rate). ABR encoding is desirable for users who want the general benefits of VBR (optimal frame-to-frame rate) encoding, but with a relatively predictable file size. Accurate ABR encoding generally requires two-pass encoding, as in the first pass, the encoder has no way of knowing which parts of the audio or video require the highest bit rate to encode.
Advantages and disadvantages of VBR The advantages of VBR are that it offers a better quality / footprint ratio than a CBR file with the same data. The available bits are used more flexibly to encode audio or video data with greater precision, with fewer bits used in less demanding passages and more bits used in difficult-to-encode passages. The downsides are that encoding can take longer because the process is more complex and some hardware may not be compatible with VBR files. VBR can also create problems during transmission when the instantaneous data rate exceeds the data rate of the link. These problems can be avoided by limiting the instantaneous bit rate during encoding or (increasing latency) by increasing the playback buffer. In the past, many hardware and software players could not correctly decode VBR files, in part because the various VBR encoders in use were not well developed. This led to the common use of CBR instead of VBR for compatibility reasons.
