(Without physically breaking, burning, or cutting, of course.)
Suppose you ask me for some data, let’s say some .jpg and .mp4 files, and I copy it onto a DVD-R disk and hand it to you. Is there any way you would be able to corrupt or alter its contents in the normal course of trying to view it on your computer?
For example, what would happen if I had given you a 9Gb disk but your DVD drive only goes up to 4.5Gb? What if you put it into your DVD drive upside down? Or let’s just suppose you have an old computer and your DVD drive is wonky, sometimes it works right and sometimes it doesn’t, without any identifiable pattern or explanation-could that damage the disk?
If you’re asking about unintentional alteration, it usually happens through mechanical failure of the spinning process: you didn’t put the disc into the slot just right, or maybe you moved your computer from horizontal to vertical while the disc was spinning, etc.
I’ve heard stories in the past of fast DVD drives spinning cheap discs so quickly that they fragmented in the drive, but that isn’t common.
I think all DVD drives read double-layer discs (9GB). Some can only WRITE a single layer, but I believe all can read it (because DVD movies from Hollywood are often double-layer).
Besides that, it would take some really wonky work with the laser to actually scribe something new onto the disc. It’s hard to imagine that happening by accident unless there’s some serious mechanical/electrical failure or some such.
If the disc isn’t ‘finalized’ then yes, you can mess up what’s on it. Even though you can’t re-write the actual data on a DVD±R disc (like on a DVD-RW) you can add data (if there’s space) and modify the table of contents to ignore the original info (essentially ‘deleting’ it). As far as putting the disc in wrong and physically damaging it, I suppose it’s possible, but it isn’t very likely. Even recordable DVDs are pretty hardy when it comes to that. And you’d be able to see that kind of damage.
But adding data to it (as a multi-session disc) would require deliberate effort, wouldn’t it? It wouldn’t just happen on its own; you’d have to try to burn something extra onto the disc?
I’ve ruined a number of discs by putting them in client’s machines.
They neglected to tell me that they jammed something into the drive in an attempt to extract a stubborn disc, bending the optical carriage enough to scratch the surface of the disc.
But, you’d know if this was happening - it makes a terrible sound…
Everyone should be aware of the fact that all optical recordable disc drives have a tiny hole on the left side below the tray which serves as a ‘manual eject’. It is designed to stick a paper clip into and will force the tray to open with no damage to the device or disc…
The OP said no physical damage, as in, mechanical from a bad drive.
But, could data be corrupted post burn? Back in the day, the first wave of CD burners, one could do what was called an “over burn”. You’d use a CD and re burn it, not all drive firmware or drivers would stop that from happening. As you can guess, the burn process would begin again and the data would be toast. Just absolutely fail the check at the end.
Another option could be a drive that has buffer issues or the like and simply write poor data. Usually the drive would alert the user but if it did not the data would be corrupt one way or the other. I remember writing music CDs that would have an audible skip due to that.
Just because those mp4/avi/mpg (or whatever format) files work on your PC, does not mean, that they will play/work on every other PC. They may not have the right codec/program installed to read these mp4/avi/mpg/etc… files.
CD/DVD’s can also be “formatted” in some weird format, which requires this certain software to run to be able to read that CD/DVD - however, this is getting more and more obsolete.
Sometimes CD/DVD’s are not finalized - meaning, that you can write more files onto the disk. Many times people are not even aware of this. Putting this disc into your dive and then a “modifying” it and rendering the disc useless can happen and does happen.
If you burn less onto a DVD then the maximum capacity of the disk can hold, then it will just contain the files you wrote onto it, eg: a 500ml glass can contain up to 500ml, but anything up to 500ml will fit into the glass as well - its just not full. However, unlike the glass, a finalized CD/DVD can not be topped up to after it’s being burned.
That’s the only thing I could think of, but it would be pretty hard to do accidentally nowadays. You’d probably have to deliberately override some sort of detection.
If you hacked the firmware of your DVD writer you could deliberately order the head to move to previously burned tracks and turn on the laser. Some DVD drives have firmware that can be edited by a special program running in Windows.
I would imagine this might corrupt the data - I know a DVD-r’s dyes are supposed to be “write once”, but how do they respond to a second or third pass?
Toast.