Can you encode an mp3 file with multiple bitrates?

Question

Is it possible to encode an mp3 file using multiple bit rates?

e.g., 0-2min 64kbps, 2-4min 128kbps, and 4-10min 64kbps (the middle section needs higher sound quality)

Or am I stuck having to encode it all at the highest?

Answer 1

I think you are looking for the term variable bit rate, more info here.

Answer 2

Yes. See the following:

Variable Bitrate @ Wikipedia

You will either need an encoder that supports it, or, if you are emitting frames on your own- you can vary the rate per segment as you wish.

edit:
Also, you may have better luck looking for resources using the VBR (variable-bit-rate) keyword.

edit (caveat):
You should note that there are potentially two different concepts in conflict here, as mentioned by sellibitze.

A higher bitrate allows the capability of storing more audio detail, but doesn't do anything for the fidelity of your recording. If your recording was already of low quality, higher bitrates will only help preserve the level of fidelity available in your audio sample.

Answer 3

Does the middle section need to be higher quality or just higher bitrate to maintain constant quality. If it's the latter you get it with a decent encoder in VBR mode (variable bitrate). If you want the quality of the middle section ("region of interest") to be higher I don't think it's that easy. In theory you can encode the track twice and mix & match afterwards. But mixing frames is not that easy due to the bitreservoir.