The customGPSvideo won't work for me either and I don't think we should need a module since they removed the functions module that was required earlier in ARMA2.

For example the playVideo works perfectly without any module so I got a feeling that some things here aren't quite complete yet.

However I went to the functions_f pbo in ARMA3 and unpacked it and did find the customGPSvideo.sqf so it's indeed there ...maybe we only have to wait for BI to get their stuff together.