Convert UNDF to MP3

Occasionally, the VLC Media Player will generate an error message stating that the UNDF multimedia format is not supported. This prompts some users to attempt converting their media files to other formats, despite them being absolutely fine. Such error is displayed if the VLC Media Player doesn't have a suitable decoder installed for the audio format.

Audio files in MP3 format can occasionally trigger such error messages. No need for a conversion in that case. All you need to do is to look for a newer VLC Media Player version, or its codecs. This issue can occasionally be caused by partially downloaded files; in such case, you should either complete the download process or download the file again.

Simply put, it is impossible to convert UNDF to MP3 directly.
Thus, there is no so-called undf to mp3 converter or a free online .undf to .mp3 converter to be found.