conversion should be synonymous with format-conversion
convert should be deleted or made a synonym of conversion
Should video-conversion be a separate tag, or should this be rolled into 'conversion/format-conversion' as well?
A related tag, file-format, seems like it might be able to stand on its own.
Seth's comment pointing out the weakness of 'file-format' seems valid. It would have to be more clearly defined. Could be related to questions on particular file formats -- e.g., tarj, gzip, 7zip, iso, cue, xml, csv -- that are not conversion questions, but use or content or programamtic interaction questions. Which isn't to say there's not a better overarching tag for those, or that the tag is necessary.