I can not reproduce the stop.
You are likely experiencing a know issue, can you please post:
OS
Browser Version
Proxy/Firewall settings (if any)
Download Speed (http://www.speakeasy.net/speedtest/)
Specific videos tested
Does it timeout at the exact same time each time played using the same browser?
Does it timeout at the exact same time each time played using a different browser?
Sorry for the inconvenience.