Help! What is the problem with playing the videos I embed here?

I keep getting email like this:

... I am having a problem viewing videos that you embed there. When I click them, it loads and plays the first 2 seconds and then stops and will not go further. Also there is no sound.

If I click through to YouTube and attempt to view them there, the same thing happens, always with no sound.

I am a fairly competent computer user and view online videos frequently – either on blogs or through YouTube directly. This is the only site this happens on. I can’t figure it out. It seems to download the entire clip but will only play the first 2 seconds. If I drag the progress bar, it will show a frame later in the clip, but only play 2 seconds from that point and then freeze again. And again, with no sound.

Any ideas? Has anyone else mentioned this?

The answer to the last question is yes. Any help? I think this is only happening with Firefox.