Bullet subtitles are basically short comments that scroll over the video at a certain point in time in the video; they allow for commentary more localized to sp

Bullet subtitles are basically short comments that scroll over the video at a certain point in time in the video; they allow for commentary more localized to specific events in the video. The first popular (and first, afaict) place where bullet subtitles have been used was the NicoNico Douga Japanese video streaming web service.