Keeks

I have found when using Express Burn that when i add clips to burn to a DVD most of the running times for the clips shows 00,00,00. When i first used it i just deleted the clips thinking they must be the wrong format or something, them i decided to write a disk as a test and found all the clips were written perfectly, what caused the duration list to not show the clip length, the type of clips makes no difference such as FLV etc some showed their running time and some didnt,which makes it hard to judge just how much can be burned as the green contents bar at the bottom of the menu does not show the real ammount to be written.Hope someone can explain this issue.