I got the answer
Both version 0.8.1 and 0.8.0 work well after I set the video size as 640 x 480. I checked the website of the webcam company, and got to know the camera supports 640 x 480.
One tricky thing is that we have to leave a space character between the two numbers. VLC crashes my windows XP if there is no space, or the video size is not set at all.
But I still don't know how to set sdp file. The log is as follow after I set sdp parameter:
stream_out_duplicate debug: * adding `std{access=rtp,mux=ts,url=127.0.0.1:1234,sdp=file:///C:\abc.sdp}'
main debug: stream=`std'
main debug: looking for sout stream module
main debug: probing 1 candidate
main debug: set sout option: sout-standard-access to rtp
main debug: set sout option: sout-standard-mux to ts
main debug: set sout option: sout-standard-url to 127.0.0.1:1234
main warning: option sdp is unknown
stream_out_standard debug: creating `rtp/ts://127.0.0.1:1234'
stream_out_standard debug: extention is 1:1234
stream_out_standard debug: extention -> mux=(null)
stream_out_standard debug: using `rtp/ts://127.0.0.1:1234'