Solution:

Actually the vedio capture support real time performace , that means 30 fps output to monitor for NTSC format and 25 fps for PAL format . However the performance depends on the AP , simply say if the signal output to CRTdirectly , so that it is real time performance, if the application is for vedio conference , so that the performance depend on modem bandwidth, CPU speed , lan protocol, and transfer rate ... etc. Regarding the 4 channels performance, that is the same as only one channel perform if the vedio input from one channel and the other 3 channel stop at one time . And that is 30/4 fps if it is switching for the 4 channels .