i am making a little movie and i want to know which frame size is usually used in dvds if it was widescreen? e.g. is it 720x576.
For PAL DVD's, yes the usual resolution is 720x576 (16:9 or 4:3). For NTSC it is 720x480. Those are not the only acceptable resolutions though. You can also (for PAL) use 352x288,352x576,704x576. But it is not common, at least not on commercially produced discs.
It's also worth mentioning that anamorphic widescreen is only supposed to be used in 720x576 or 704x576. If you encode anamorphic in one of the other resolutions your DVD player may not play the title at all.
