Dust can collect on the lens in your DVD and CD players which causes difficulty in playing disks correctly or for them to not play at all. I used to always blame the disk in having flaws or scratches but when your video skips a lot it may be indicating that it is time for cleaning the DVD and CD player.
Cleaning disks are available at any of the electronics stores. Many have little brushes on the backside of the DVD or CD. The disk spins when placed in the player and the brushes act to clean the dust from your laser lens.
To use the cleaning disk, just place it in your player and allow it to detect it. Then hit play and it will start to play the disk. It should run for only 15-20 seconds and then stop. Finally, you can eject the disk and your player should be clean.
It is recommended that you repeat it for every 8 hours of play. I would just do it when your images or music starts to skip. Take note that these should not be used on gaming systems that use a DVD as it can damage the system.