According to manufacturers' data and technical literature, thirty years appears to be the upper limit for magnetic tape products, including video and audio tapes.  Actual experience may vary depending on how tapes have been maintained. An article in the June 1995 issue of Scientific American says the “physical lifetimes for digital magnetic tape are at least 10 to 20 years.

Any videotape that is over ten years old is on borrowed time, but every videotape should still be stored in a way to maximize its ability to preserve the images and sound recorded on it. The first thing to do is to keep the tapes in an environment that is as temperature and humidity stable as possible. A room that is regularly used by people is probably acceptable. If the room is a storage room that gets hotter or colder than the rest of the house it probably is a bad choice. An attic or garage used for storing videotapes is just accelerating the degradation process. There are many issues that cause videotapes to degrade.

Physical Breakdown of Tape

The adhesive layer of a videotape that holds the magnetic particles in place breaks down and becomes sticky, making it un-playable. This condition is known as “sticky tape syndrome”. A clear indication that a tape has this problem is when a tape will not uncoil freely and feels like you are pulling off a piece of scotch tape. I have encountered many tapes with this problem, particularly Hi-8 generation videotapes and reel-to-reel audio tapes.  There are some advanced procedures (baking or refrigeration) that can be used to attempt recovery of sticky tapes, but they are expensive and often unsuccessful.

Demagnification of Tape

Information is stored magnetically on videotape, therefore a strong magnetic field will erase the tape.  Long exposure to weaker magnetic fields generated by televisions, speakers and electric motors that are running are also a threat to video and audio tapes. A simple fix is to not store tapes under television sets or next to speakers, and not to run electric motors (such as fans) close to them.

Storage of Tape

Keep videotapes in the box that the manufacturer or vendor supplied - never store them outside of their boxes. Store videotapes upright and lined up on a shelf or in a container as if they were books on a library shelf. Keep them away from exposure to high levels of dust or liquids. Never store a videotape inside a playback device.

Ironically, even playing a videotape causes it to degrade due to the moving parts of a playback machine coming in contact with the tape. The bottom line is that no matter what the brand of videotape is, no matter how well they have been kept, the information recorded on those tapes will not last forever. Little by little every single day the magnetically encoded information on the tapes is being lost.  The most effective way of preserving video and audio tapes is to have them digitized.