We often see people trying to edit existing DVD-Videos. Some seem to be able to do this fine, while others struggle mightily. What’s the deal? Why can’t one just Import those VOB files and edit happily away?
Let’s go back to the basics just a bit. A .VOB file is a "Video Object File." As such, and by the DVD-specs., it can contain quite a bit of stuff. Some of this is beyond just the Audio & Video contained in the usually present MPEG-2 file, which is hidden inside the VOB. This VOB can contain subtitles, Menus, and ROM content, to name but a few. With simple VOB’s, one can often play them, if they are just renamed to .MPEG, though not always. In the case where this works, one does not need a DVD software player. Any player program that can handle MPEG-2 can play the file.
The structure and elements of a DVD-Video DVD-5 (4.7GB, single sided, single layer) will be in most cases:
AUDIO_TS folder (usually empty). May also not be present.
VIDEO_TS folder, which contains VIDEO_TS.IFO (Video Manager.info), VIDEO_TS.BUP (VMGI.backup), VTS_01_0.IFO (Video Title #1.info), VTS_01_1.VOB (Video Title #1.video), and more of these, incremented by 1. Depending on the number of "titles" on a particular disc, the numbers can range up to the limit of 99. For Projects from most NLE/authoring programs will only have one "title," so you’ll likely not see more than 4 VOB’s and their accompanying IFO’s and BUP’s. The VOB’s will be approximately 1GB in size, the upper limit.
The title of the "movie" inside the VIDEO_TS folder will be contained in the .IFO and the BUP files. If you open up a DVD-Video in Windows Explorer, you’ll see just the folders, and no name, or anything else. The same is for the file names inside the folder(s). They will look the same for all DVD-Videos, though the exact number of these will differ, depending on the structure and number of discrete titles on the disc. It’s not until one opens the DVD-Video in either a software player, or in a set-top player, that the IFO files will play, allowing the player to then access and work with the .VOB’s, via the instructions that are contained in the IFO and BUP files.
Editing a VOB can be a tricky, as it can contain all those different things. Ripping the MPEG-2 file from the VOB is usually the best approach. That is what PrPro, PE, or other NLE’s (Non Linear Editor) attempt to do. Sometimes, it works fine, but sometimes it does not. Another problem can be when there are multiple VOB’s, as the MPEG-2 files can span multiple VOB’s, as they cannot contain more than about 1GB of data. This is why a DVD-Video can only have 1GB of space for ALL Menus and their elements.
As VOB’s can contain the full menuing structure (this will be the first VOB), unless this structure is done 100% by the DVD-specs, there will be issues. Most DVD-recorders include some form of menuing, and most do not do it perfectly. This WILL create issues. Ripping via software will likely be the only answer, or doing a manual capture from a set-top DVD player, hooked up appropriately to your computer with a capture card, or bridge, and using the software that came with that device. You will not have any "device control," so you must start the capture software, hit Record, and then start your DVD in its player. If you do this, make certain that you capture to DV-AVI Type II w/ 48KHz 16-bit Audio.
Once one has edited the Audio & Video contained in the .VOB(s), the process to get the resulting Project back into DVD-Video form is to Burn to DVD. This is the authoring process.
Three things happen:
1.) The edited file is Transcoded to MPEG-2. If you were working from a VOB already, the Audio & Video material has already been Transcoded to MPEG-2, in which there will already be compression of the data. If you do this again, there will be more compression of the data, resulting in a loss in quality. Some NLE’s can do "smart rendering/encoding." None of the programs from Adobe can do this, as they are designed to work with material captured from a miniDV tape camera. While they can handle other footage, there will be compromises. When designed, DV-AVI Type II was chosen as the base workflow, because that was what most miniDV tape cameras produced. The introduction of flash memory, miniDVD, and hard drive cameras, plus the introduction of HD, has changed things a bit, and will continue to change them over the next versions of the programs.
2.) The folder structure and the necessary files are created.
3.) The above material is then physically Burned to a DVD-Video, or is copied to a folder on the computer in the required, and necessary form and structure.
In the case of the former, one can then play the DVD-Video via a software player on a computer, or on a set-top player hooked to a TV or display device. In the case of the latter, one needs a software player to play the files in the VOB, with the instructions coming from the IFO, or the BUP files.