What makes a good layer break?

[ParticleMan]

I'm burning dual-layered DVD Videos and I'm not sure where I should place the layer break. I know that the layer break must occur in certain places (either before certain files or at an entry point to a cell), but what makes certain locations better than others? ImgBurn gives me several options and rates them, but what does ImgBurn use to rate a certain location (e.g. how does it know that one sector is a good sector and an other is merely average)? Also, do I need to change the IFO/BUP files to reflect where the layer break is?

[Ghitulescu]

There are technical issues and perceptual issues.

Technical issues are laid down in the DVD book. Perceptual issues depends entirely on you. Since the layerbreak is usually associated with a slight pause (some bluray players need up to 2 seconds), it may be desirable to place it within a still image, or a scene change, or even better between physical files.

[ParticleMan]

So am I correct in thinking that a layer break in between files is always better than one at the beginning of a cell?

[Ghitulescu]

Yes..

[r0lZ]

I know that ImgBurn uses a similar algorithm than PgcEdit to find out what cell or file it is best to recommend. If PgcEdit or ImgBurn can put the LB at the beginning of a file, they will (almost) certainly propose that position by default. But it's rarely possible with movies, as the movie occupies often more than half of the disc space, and therefore must be split somewhere in the middle. (For episodes or collections of shorts, of course, it's exactly the opposite: it is almost always possible to propose a totally "invisible" LB point.)

When a DVD has been copied on disc, the position of the original LB is lost, but sometimes, there are remnants of that position. (For example, the Seamless Joint flag may still be clear if your ripper program doesn't set it by default, or there might be a VOB ID change in the middle of the title without apparent reason, and they are good indication that the LB was probably there.) If PgcEdit or ImgBurn can find one of there remnants, they will consider that point as (probably) better than the other points.

Finally, if it is impossible to guess where the original LB was, the programs consider that it is probably best to place approximately the same amount of data on both layers, and therefore they will pre-select the point that is near the middle of the DVD. But in that case, although technically it's a good choice, it might not be a good point, if, for example, it is just in the middle of an action scene, so you have to experiment with the preview to see by yourself if it is really suitable.

BTW, when it's still possible, I continue to use the good old DVD Decrypter to rip the DVDs, and it doesn't clear the "layer break" (in fact the "Seamless Joint" flag), and therefore the position of the original layer break can easily be found. Of course, you can still change it manually if you wish.