vuforia视频播放4.2.3，删除参考图像时视频消失

I'm using vuforia videoplayback 4.2.3 for playing a video in texture. It works fine as long as the reference image is kept. But if the reference image is removed the video disappears. My requirement is to continue playing the video even if the reference image is removed. I enabled "extended tracking" but nothing happened. In many youtube videos I saw 3D images working after the reference image is removed but not for videos. Pls help. Thanks.I'm using vuforia videoplayback 4.2.3 for playi