Is U.S. iPad HDMI "international" format for output?

It should be no issue.

Living in a PAL country, I do not have experienced any problem since I got my first digital LCD TV many, many years ago. NTSC works as does PAL.

Still, for instance Lifewire points out that there still are differences:

The thing is that I do not see issues. TVs work both with PAL and with NTSC and I would guess that SECAM does not make any difference.

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