small change to make code fit for ubuntu in VB

Small change in the use of gstreamer, making it fit for ubuntu in virtualbox. I have tested on my virtual mechine, and record the main process in README.md.  *I`m a Chinese, if I made any grammatical mistake, please correct me  ^_^. Any question or suggestion, contact:Email: jpflcj@sina.com or jinpengfei@cstnet.cn*