[Feature Request] VBR conversion

Description

I would like a feature for converting songs to M4A (AAC) 320khz Variable Bitrate aka VBR format. This could be eg. a VBR toggle next to the bitrate.

Use Case

Older Ipods (tested on Ipod nano 5) require this format to function properly. The non VBR files have a kind of chirping sound in them at fix timestamps.

Additional Context

This is the current setting, there is no VBR.