I'm in complete agreement with Jeff here as well - selling PAL discs in the US will sooner or later cause problems.
Priobably sooner.
In the old days you would not get the player to even load them - it would throw a "no disc" or another error of some description - and even when you did find the odd rare one that would load them, the TV systems would make sure you got a garbled image, or a B&W one. These days a good Universal Player will usually load all types (although again a regular DVD player will most likey still not go for it) but you will still have TV system issues.
The problem is the mains frequency - PAL (Europe) uses 625 lines and 50Hz whereas NTSC uses 525/60, which effectively means PAL runs at 25 frames/second & NTSC at 30 frames/second. The 2 are incompatible. Most PAL players can handle both formats either by outputting NTSC discs as PAL-60 or even genuine "on the fly" conversions to 525/60 NTSC. The process is not straightforward either - the player is handling scaling, temporal conversion and object motion analysis all at once (Hence why most PAL setups output NTSC as PAL-60 instead of pure 525/60 NTSC) and additionally the audio speed must be adjusted (remember DVD is a multiplexed set of VOB files, not separate streams) to conform to the different display rate - which may also prevent the use of a digital connection!
This type of conversion is much, much less compatible the other way around. Most NTSC players still cannot play PAL discs (although as I have said a Universal BluRay player may do this) and only a very small number can convert 625/50 PAL to 525/60 NTSC.
Let us now talk about MPEG audio & why it is not recommended to use it. This gets complex.....
MPEG audio is a multichannel format using perceptual encoding at 16-bit 48KHz. MPEG-1 Layer II and MPEG-2 BC (backwards compatible) are the only allowed forms and the MPEG-2 that is allowed - BC - is a matrixed format, not discrete, in surround use. Use of this type (MPEG audio) was only ever optional in NTSC, never mandatory (so that is one big problem) and the other big problem is that MPEG-2 audio is only allowed in BC mode. Why is this evil? Take a seat & let me try to go through it.
Because MPEG-2 audio decoders were not available at the time of DVD introduction, MPEG-1 was the only decoder available so that was what got used. As a result, the only permissib;le type of MPEG-2 allowed is BC, which is a matrixed stream type (the 5 main channels are matrixed into Lt/Rt stereo streams) and then encoded in the normal MPEG-1 Layer II format for DVD. The advantage to this is that a multichannel stream can be phase matrix encoded so that it will also play on a stereo system. MPEG provides pre-determined matrixing formulas depending on the intended audience - one is a conventional stereo signal, another is designed to deliver a Dolby Surround compatible (*not* Dolby Digital - that is something very different) system that re-creates the centre channel fronm the left/right channels in addition to a single rear (or surround) channel (Nerdy Note - this is actually a development of the old SQ Quadraphonic matrixing system, set up for LCRS instead of L-R-Ls-Rs). Additional discrete channel information, plus the LFE channel, is encoded in an extension stream so that an MPEG-2 decoder (not MPEG-2 Audio) can recreate 6 separate signals. Because of the necessity to be backwards compatible with MPEG-1 decoders the centre & surround channels that are matrixed into the 2 MPEG-1 channels (left & right) are duplicated in the extension stream. This allows the MPEG-2 decoder to subtract those signals from the matrixed signals, leaving the original Left & Right channels. All this adds an overhead of approximately 32kbps, making it rather inefficient.. The original 2-channel MPEG-1 encoding process was not developed with matrixed audio in mind and therefore may actually remove surround detail. Also, the process tends to expose coding artefacts as well so coupled with the whole shebang only ever being optional in NTSC 525/60 systems means that to use this as your solitary stream type is actually out of spec for 525/60 regions & players may well take one look at the disc & output...................in short, just a picture. And if that picture is 625/50 PAL, quite possibly not that either.
Audio support in DVD.
MPEG-2 audio is basically not supported except in BC moide, which hands everything over to MPEG-1 decoders. This is not good. It is not efficient, it can be riddled with artefacts & it is not supported by fiat in NTSC regions, only optionally. If it is your sole stream you will run into trouble sooner or later.
I hope this helps, and I think I will go away & write a little article about this as it keeps cropping up every so often..