Conversion of undf files to flac file format

Undefined (UNDF) file types are typically partially downloaded, corrupted, or occasionally labeled as unknown by VLC player. Unless the file is actually just renamed audio file, there is no way how to convert or recover that to FLAC. If you think the file is definitely audio, try to rename it to FLAC and play, if that doesn't work then there is really nothing you can do and no undf to flac conversion is going to change that.

Open UNDF file    Open FLAC file