为什么MediaElement有时会无声地失败，我该如何纠正呢？

In my WPF project I have created a view that includes several MediaElements playing videos. Sometimes, anywhere between one or all of the MediaElements will fail to play the video assigned to them, and will instead show a black rectangle, or not appear at all. The MediaFailed event does not occur when this happens. The MediaOpened event DOES get raised on all the MediaElements, even when they do not play the video. In my WPF project I have created a view that in