4 of the 7 weddings shown are real, but those ones are only shown for a few seconds each towards the end, so the video is NOT entirely fake. The director did a Twitter callout to grooms who wouldn't mind a band coming to their wedding to shoot a scene for a music video that would double as a surprise performance for the bride and guests. At these weddings, Adam and James also performed She Will Be Loved for the couple's first dances, there are postings on IG and Twitter from guests/photographers, etc of these weddings that show this happening and that it was in fact a surprise for them to be there. So the rigging was already set up for these "surprise" music guests to come in and play and they did 2 takes, the original one of them coming in the first time and then a second more "lively" shot to get more angles. They filmed it over 3 days. It's not that hard to find all this out, you just have to look further than major publications to find it.