Totally depends on the burning software, the write speed of the optical media/disk and finally the performance of your system, CPU, RAM, Hard Disk, etc.
If your system isn't particularly fast you often get pauses in the burning as the data is read/copied from the hard disk to the burning software and DVD. Then if your burning software is capable of burning at the max speed of the DVD write speed.
Generally it isn't a good idea to try for the max speed possible (which is more prone to errors and converting DVD into coasters), but to back off a bit to ensure it gets done without error.
