They're Not Really PAL or NTSC
The first thing I need to clarify about DVD is that PAL and NTSC are words and formats that are applied to DVD for convenience, and because of historical convention. There is nothing fundamental about a DVD which makes it either PAL or NTSC, but for simplicity and brevity, I will continue to use these terms throughout this article.
At their heart, DVDs are merely carriers of data files with compressed audio-visual information contained therein. This information can be placed on DVD in one of two resolutions; 720 x 576 pixels (PAL DVDs), or 720 x 480 pixels (NTSC DVDs), and with various frame rates (24, 25, and 30 frames per second are common). The DVD player itself takes this data file and formats it appropriately for display in either PAL or NTSC.
http://www.michaeldvd.com.au/Articles/PALvsNTSC/PALvsNTSC.asp
i think replay is normally decode in MPEG2. maybe now everything is multi system, region free.