预览的尺寸和视频录制的尺寸是一样的：
mCamera.setPreviewSize(UVCCamera.DEFAULT_PREVIEW_WIDTH,
UVCCamera.DEFAULT_PREVIEW_HEIGHT, PREVIEW_MODE);

                             private static final int VIDEO_WIDTH = UVCCamera.DEFAULT_PREVIEW_WIDTH;
 private static final int VIDEO_HEIGHT = UVCCamera.DEFAULT_PREVIEW_HEIGHT;

        final MediaFormat format = MediaFormat.createVideoFormat(MIME_TYPE,
            VIDEO_WIDTH, VIDEO_HEIGHT);