Thanks!
I have confirmed the selection is correct. I use 640*480 15pts for preview but 2048*1536 15pts(i have written wrong for this framerate in the answer). I check in the logcat and console print. The ov3640 has two work mode: one is QXGA mode for full pixel and 15 framerate, the other is XGA mode for 1048*768 and 30 framerate. I only use QXGA mode for preview and capture, in order to avoid mode switch. I just set the register of crop, zoom and output size for the resolution mode changement. Is this correct?