Average bitrate (ABR)
Average bitrate encoding aims for a target average file bitrate while still allowing some parts of the file to use more or fewer bits.
What it is
ABR stands for average bitrate in many audio encoding tools. Instead of forcing every frame to use the exact same bitrate, the encoder can vary the bitrate locally while trying to finish near a target average such as 128 kbps, 192 kbps, or 256 kbps.
This makes ABR a middle ground. It gives more size predictability than pure VBR, but more flexibility than strict CBR.
CBR vs VBR vs ABR
| Mode | Best thought of as | Typical use |
|---|---|---|
| CBR | A fixed bitrate budget. | Compatibility, broadcasting, simple pipelines. |
| VBR | A quality target with flexible bitrate. | Music libraries and efficient storage. |
| ABR | A target average bitrate with some flexibility. | When file size matters but strict CBR is unnecessary. |
How Huffman coding relates
Huffman coding does not decide the user's bitrate setting. It helps determine how many bits the encoded symbols need after the codec has analysed, transformed, and quantized the audio.
If a frame's quantized data is easy to code, Huffman coding may describe it with fewer bits. If it is harder to code, it may need more bits. ABR-style rate control can take advantage of that variation while still aiming for a chosen average across the whole file.
Not the same as adaptive bitrate streaming
ABR can also mean adaptive bitrate in streaming video. That is different. Adaptive bitrate streaming prepares several versions of a video at different bitrates and lets the player switch between them as network conditions change.
On this page, ABR means average bitrate encoding.
LAME branch notes
In LAME MP3 use, ABR is useful when you want a predictable target such as 128, 160, 192, or 256 kbps while still allowing the encoder some local flexibility.
The lamemp3.co.uk branch notes also expose --bitrate-boost in ABR mode at level 1. This should be described as an advanced allocation option, not as a replacement for ordinary ABR decision-making.
lame --abr 192 --bitrate-boost input.wav output.mp3