How to convert .bnk videos to .wma format.
Converting Bink Video Files directly to Windows Media Audio Files (.bnk to .wma conversion) should be possible and relates to users attempting to extract the audio track (WMA) from an BNK video.
It appears that your options are limited and that your best bet could be using the Freemake Converter, which allows users to import BNK videos and re-save them in WMA format.