The BrookTree is a video capture chip (as in for viewing TV) that is well supported by Linux and the BSDs. The brooktree chips come in many varieties, such as the Bt848 / 849 / 878 / 879. Once upon a time the datasheets were publically available for these chips, apparently, hence the good driver support in Linux and the BSDs.
To watch video, you probably want to use a piece of software like xawtv. On the cards that have an FM tuner present, you can use xmradio to get the audio stream.