hello ! I met a problem. use the following command line for video preview ffplay.exe -framerate 5 -video_size 320x240 -pixel_format 0 -f dshow -i video="Logitech QuickCam Pro 4000":audio="USB Audio Device" I find "framerate 5" doesn't work, Video acquisition is according to about 20 frames per second to run How can i solve this problem?