On audio and video cassettes there is always a stretch of leader tape–a length of plastic tape–at each end of the tape. When recording, you have to wait for the leader tape to play through before you hit the record button. It seems that adding the leader complicates the manufacture of cassettes since you have to splice it onto the magnetic tape. For tapes sold for consumer recording, it is a pain to time your recording.
Why does the world need leader tape?
Even when a tape is rewound a small portion of tape is exposed at the bottom of the cassette. (Yes, on a video tape the tape is covered by that little flap, but if you look at the tape from the bottom you can still see the tape.) Since it is exposed, this portion of the tape can collect dirt, scratches and other damage. Leader tape prevents the damage from occuring on the potion of the tape that actually contains a recording.
Also, on VHS tapes in particular, a large part of the tape has to be pulled into the mechanism before it can start playing or recording. The leader allows for this in that you won’t have something recorded on a portion of the tape that will never be able to get to the playback head.
The same holds for reel-to-reel tapes too. The leader (or trailer, since reel-to-reels are normally stored “tails out”) is the outside of the tape when it is stored and you have to have enough tape to thread through the mechanism without losing recorded information. Reel-to-reels also had a habit of breaking at the ends and the leader allowed for the occasional loss of tape from the end without affecting the recording.
sometime leader tape is very useful
in some tapes, leader tape is made of some non abrasive material which cleans the head as it moves over it
so each time u play the tape, the head is cleaned
Leader tape is much stronger than the recording tape.
If you used recording tape right through to the reels it would break upon rewind and forwarding functions.
Leader tape is designed to take these stresses, if you look you will find that leader tape is of such length that it wraps around the whole of the reel in such a way that the recording tape is never subjected to the full forces of ‘end stop’.
Also, VCRs have a sensor to detect when the beginning or end of a tape is near so the appropiate motor can be stopped. This saves excessive stress on the tape and the motor. Get an old videotape, remove the clear leader and re-assemble the tape. Wind it forward a little bit and then rewind it. You’ll notice a difference in how the machine sounds when the now-leader-less tape gets to the end.