Bcam use two different TCs. The LTC (longitudinal Time Code) is a digital signal that get recorded in a separate track the same than the audio. VITC (Vertical Interval Time Code) is a similar signal that get recorded in some of the first line of the image that have not picture information (this is why some times we can see small white dots moving in the top of the picture).
Normally they are use toghether. They should have the same time information (although some times it doesn’t happen and make the editor crazy).
The LTC is easier to read in Play or FFW & REW and the VITC normally is readed when the tape run slow or is stoped (In that momment the LTC can not be readed because need certain tape speed). Usually the two of them are enabled and the desk use the one that can read esylly, but you can give prioriti or disable bouth.
Two download BCam footage to a Mac you must do it through a videocard, and to record the original TC of that footage, the videocard has to allow you to do that. I guess that the VITC of the Bcam became just a part of the image (white dots) when the image is captured, but it doesn’t as as a TC any more.
To put footage back to Bcam we got the same issue with the TC (LTC or VITC). The video desk can record a TC that generate it self or can record an externall TC if you provide it. When you print to video in DV, the TC signal goes thrugh the FireWire but, How to rout this TC signal to your Bcam desk? No idea.
In the end is a matter of send the TC (LTC or VITC) to the computer and back. I think is a matter of video cards.
I hope I didn’t confused more.
salud,
Rafael