Tony
I appreciate and understand what you are saying, but just as a matter of interest you can re-select PAL or NTSC at any stage before starting the actual transcode.
If you have say a five minute clip then that would be ideal to play around with.
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This was something I put together sometime ago just to explain how to "join" and burn a movie to DVD format.
So some of the items need not apply.
Hopefully it may be of use in the future:
Using Nero 6 to join and burn two or more movie files "avi, mpeg, DivX, Xvid" (any movie file) into one movie.
(Some parts listed below are just my own personal choices as I want chapters, but without a menu or having to create them manually)
Nero's default will create chapters every two minutes, which is not as bad as it may sound.
From Nero StartSmart
1. Select "DVD", followed by "Make Your Own DVD-Video"
2. Select "Add Video Files"
3. Select the files you want to merge and burn and press "Open"
3. The files are now in view and highlighted, (if not highlighted press and hold Ctrl then select the movie files)
4. Select the MIDDLE icon on the bottom left hand side of the screen, a message will say "Merge Titles" when you hover the mouse over it, now press it, a warning message will follow saying,
"Merging titles means that a new title is created from the contents of the selected ones, which are then removed from the document. Do you want to continue?" Yes/No.
... (Make sure the files are listed top-to-bottom in order)
5. Select YES (your original files will still be intact when finished, it does not delete or remove them).
You will now see only one title with the original file name, except the time of the movie is now for all parts.
From here (a personal choice) is to select "More>>" and place a tick in "Create chapters automatically" (this will create chapters every 2 minutes).
Also at this point you can also select which format you want your movie in "PAL/NTSC".
Then press "Next"
6. Now at the top right hand corner select "Titles and chapter menus" and select "Do not create a menu"
Then press "Next"
After the preview press "Next"
7. You can now select where to save or burn the DVD vobs files.
(again a personal choice) I prefer to save to the HDD then burn later.
Then press "Write".
Now sit back and wait 2, 3, 4, 5 hours, depending on your PC and the size of the movie.
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There are a couple of points either missing or do not need being done from the above, that is.
1. In your case you need to re-select NTSC.
2. You do not have to merge the files into one long movie.
3. You will be selecting the first vob from each clip as your movie.
I hope this helps.