Don't get your fingers burnt with burnt-in timecode!
If you are a composer writing and recording music to picture, then you will absolutely love burnt-in timecode. You'll love it so much you'll want to kiss the guy who invented it and possibly even have his children.
Before I come on to what it is, what's the problem in the first place?
The problem is that in video recording (film as well, but I'll stick with video), picture and sound are handled separately. On the original video tape, they are both on the same medium - the tape - but to be edited, sweetened and mixed effectively, the sound has to be handled by sound specialists with their own sound-orientated equipment.
So once sound is separated from the picture, there needs to be a link so that the two can be joined back up again.
That link is timecode. Timecode labels every frame of video in hours:minutes:seconds:frames, for example 10:01:01:00 is one minute and one second into the recording. (It is a common convention to start the timecode clock at 10:00:00:00 to avoid 'midnight' or 00:00:00:00, which historically was a problem for some equipment.)
So if the video tape (or disk or computer file equivalent) has timecode, and the audio tape/disk/file has timecode, then picture and sound can easily be run in sync. So the composer can watch the pictures while recording and playing back his music in sync.
The problem is whether you can trust the equipment always to get it right. In the past, it was an impossibility. When you stop a video tape, it is impossible to read conventional timecode. So if you are looking for a hit point, as soon as you find it and stop the tape, timecode disappears.
So the equipment has to guess what the timecode value of that frame is. Not nice.
There is such a thing as vertical interval timecode (VITC) that can be read while the video is in pause mode, but in practice the better solution (or you can have both!) is to burn the timecode numbers into the picture.
So when you play the video, you see the numbers because they are part of the picture.
This is such a useful concept, it still applies to modern technology where pretty much everything is done on the computer. If you can see these numbers in the picture, then you know that the timecode value is correct. (And if it isn't correct, then it isn't your fault!). For instance, frames can be skipped during the digitization process. With burnt-in timecode, this will be evident.
So, as a music composer working to picture, you will always ask for a copy of the program with burnt-in timecode. Whether it comes on tape, disk, DVD or any other media, you will always know that the timecode values are correct.