Music Directory Syncer is a Windows application that allows a directory of music files to be synced to any number of others, according to certain rulesets:
- Tags being present
- Tags having certain values
- File type
Audio files can be converted to a chosen lossy format using ffmpeg if desired to save space, e.g. on a mobile device. This can be done to all files or just losslessly compressed ones. You can also choose to apply ReplayGain volume adjustment if the device you're using doesn't support ReplayGain tags. Once you've made your synced directory, you can use any directory syncing application to copy it to a mobile device, for example.
Music Directory Syncer will run quietly in the background watching your chosen source directory for changes, and it will update all of your sync directories on-the-fly.