Convert BNK to MP3

Converting Bink Video Files directly to MP3 Audio Files (.bnk to .mp3 conversion) should be possible and relates to users attempting to extract the audio track (MP3) from an BNK video.

It appears that your options are quite limited. Your best bet might be using the Freemake Video Converter, which allows users to import BNK videos and export their extracted audio track in MP3 format.