CBR vs VBR: Constant vs Variable Bitrate
When encoding lossy audio, you choose between constant and variable bitrate. CBR gives every second the same amount of data. VBR gives complex passages more data and simple passages less. The choice affects quality, file size, and compatibility.
CBR Explained
Constant Bitrate allocates the same number of bits to every second of audio. A 192 kbps CBR file uses exactly 192 kilobits for every second, whether the audio is a complex guitar solo or dead silence. The advantage: predictable file size and guaranteed streaming bandwidth. The disadvantage: wasted bits during simple passages and insufficient bits during complex ones. CBR is older and simpler. Some streaming protocols require it.
VBR Explained
Variable Bitrate adjusts bit allocation on the fly. A complex section might use 320 kbps. A quiet passage might use 96 kbps. The encoder decides based on the audio content. Average bitrate varies but quality stays more consistent. VBR produces better sound quality at the same average file size compared to CBR. Modern VBR encoders like LAME are sophisticated — they have been refined over decades to make excellent allocation decisions.
ABR: The Middle Ground
Average Bitrate is a hybrid approach. You set a target average bitrate. The encoder varies the instantaneous bitrate but aims for your target over the whole file. Think of it as VBR with a file size budget. ABR gives you reasonable quality with more predictable file sizes than pure VBR. It is less popular than CBR or VBR because VBR generally produces better results and CBR gives more precise size control.
Quality Comparison
At the same average bitrate, VBR sounds better than CBR. This is well-established through decades of listening tests. VBR spends bits where they matter. CBR wastes bits on silence and simple passages. The difference is most noticeable at lower bitrates (128 kbps and below). At 320 kbps CBR, there is so much headroom that the waste does not matter — both modes sound excellent. For MP3, LAME's VBR presets (V0 through V9) are widely considered the best quality-per-byte option.
Which to Choose
Use VBR for music files, personal libraries, and situations where quality matters most. Use CBR for streaming where bandwidth must be predictable, podcast hosting platforms that require it, and legacy devices that have VBR compatibility issues. Use ABR when you need a specific target file size with variable quality. When in doubt, use VBR. It has been the recommended choice for MP3 encoding since the early 2000s.