CBR vs VBR Encoding

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If you want to rip your music CDs to an audio format like MP3, WMA, AAC, etc., or need to convert between formats, then it's a good idea to know what CBR and VBR mean before you start.

Below is a primer on what these two abbreviations mean, how they work, and the difference between the two encoding methods.

Note: CBR and VBR are also abbreviations for other tech related terms like CDisplay Archived Comic Book files and volume boot record, but neither have anything to do with encoding as described here.

CBR Encoding

CBR stands for constant bitrate, and is an encoding method that keeps the bitrate the same. When audio data is encoded (by a codec), a fixed value is used, like 128, 256 or 320 Kbps.

The advantage of using the CBR method is that audio data typically processes faster (compared to VBR). However, the files that are created aren't as well optimized for quality versus storage like is the case with VBR.

CBR is useful when it comes to streaming multimedia files. If the connection is limited to only performing at, say, 320 Kbps, then a constant bitrate of 300 Kbps per second or lower would be more beneficial than one that changed throughout the transmission since it could possibly go higher than what's allowed.

VBR Encoding

VBR is short for variable bitrate and is, as you'd guess, the opposite of CBR. It's an encoding method that enables the bitrate of an audio file to dynamically increase or decrease.

This works with a target range; the LAME encoder, for example, can be between 65 Kbps and 320 Kbps.

Like CBR, audio formats such as MP3, WMA, OGG, etc support VBR.

The biggest advantage of VBR when compared to CBR is sound quality to file size ratio. You can usually achieve a smaller file size by encoding audio with VBR than CBR because of the way bitrate is altered depending on the nature of the sound.

For instance, the bitrate will be significantly reduced for silence or quieter parts of a song. For more complex areas of a song that contain a mix of frequencies, the bitrate will be increased (up to 320 Kbps) to ensure sound quality is maintained. This variation in bitrate will, therefore, help to reduce the storage space needed compared to CBR.

However, the disadvantage of VBR encoded files is that they might not be compatible with older electronic devices like CBR is. It also takes longer to encode audio using VBR because the process is more complex.

Which One Should You Choose?

Unless you're restricted by old hardware that only supports audio formats encoded using CBR, then VBR is usually the recommended method. Support for VBR in hardware devices like MP3 players, PMPs, etc., used to be hit and miss, but these days it's usually a standard feature.

As mentioned above, VBR gives you the best balance between quality and file size. It's therefore ideal for portables that have limited storage or where you want to make efficient use of other storage solutions like USB flash drives, flash cards, etc.