CBR/ABR/VBR: the 3 encoding modes


LAME is able to encode your music using one of its 3 encoding modes: constant bitrate (CBR), average bitrate (ABR) and variable bitrate (VBR).

Constant Bitrate (CBR)

This is the default encoding mode, and also the most basic. In this mode, the bitrate will be the same for the whole file. It means that each part of your mp3 file will be using the same number of bits. The musical passage beeing a difficult one to encode or an easy one, the encoder will use the same bitrate, so the quality of your mp3 is variable. Complex parts will be of a lower quality than the easiest ones. The main advantage is that the final files size won't change and can easily be predicted.

Average Bitrate (ABR)

In this mode, you choose the encoder will maintain an average bitrate while using higher bitrates for the parts of your music that need more bits. The result will be of higher quality than CBR encoding, and this mode is highly recommended over CBR. This encoding mode is similar to what is reffered as vbr in AAC or Liquid Audio (2 other compression technologies).

Variable bitrate (VBR)

In this mode, you choose the desired quality on a sqale from 9 (lowest quality/biggest distortion) to 0 (highest quality/lowest distortion). Then encoder tries to maintain the given quality in the whole file by choosing the optimal number of bits to spend for each part of your music. However, this mode heavily relies on the encoder psychoacoustic model and could lead to a few "bad choices" in the encoding process. You may want to specify a minimum bitrate (ex: -b 64) to avoid those potential errors.