[reboot]

Almost all capture devices capture in one stream. Some will only do very small aspect avi, others will allow avi or mpg, in larger aspects, and/or your choice of codecs. Some allow the flexibility of capturing in separate streams. The Dazzle 150 also allows you to cap audio at various frequencies and fps.
Depending on what you want to DO with the captured video, is how you capture it.
The dazzle is just an easy to use, versatile, device. Capture to mpeg2 directly for burning to (S)VCD or DVDR, capture to avi (with a selection of codecs) to archive, or only play on computer, and/or edit extensively before encoding.
It also comes with Pinnacle software (some of the best).