Hello UpulGunasena,
It sounds as though you have a video on your iPhone that you're having issues importing to a Mac or PC. When attempting to import are you following the steps outlined in Transfer photos and videos from your iPhone, iPad, or iPod touch? If not, please try the steps outlined there.
If you continue to have issues importing the video can you comment if the video is stored in the Photos application, or is it in a different app? If it's located in a different app you may want to contact the app developer for the best support.
How to contact an app developer
Have a great day!