What are the X-StartTime and X-TimeStamp HTTP Header values?

I am writing an HTTP proxy to serve up an M-JPEG stream from an IP camera on the LAN. I noticed that it returns the HTTP header X-StartTime: 1276943417197. With each JPEG frame, it also includes a header like X-TimeStamp: 346024130. I was unable to find anything about these headers online, does anybody know what they are?

From stackoverflow

• The X-StartTime is the number of milliseconds elapsed since 1/1/1970, just like a Javascript Date...

  javascript:alert(new Date(1276943417197));