Why does My iMac suddenly not recognise my photo and video formats

At some point in the past few months something has changed on my iMac (mid 2011 running Yosemite 10.10.5). I used to be able to sync my Windows phone with my iMac, using Windows Phone for Mac. I could import all my photos and videos perfectly. Now my iMac tells me my videos are in an unrecognised format. They are mp4 and always have been. My photos are .jpeg and always have been but sometimes I get the same "unrecognised format" message as I get with my videos. I did not realise my videos were not importing and unfortunately deleted some special ones from my phone believing they had imported as before. The message only started appearing a few days ago. Why is this happening?

I have not changed any settings and no one else has access to either my phone or computer to change settings and I can't find anything to tell me what is wrong using the Help tab. I have had no updates on my phone, only my computer. The last one was something to do with RAW camera, but I don't know what that is or what it changed.

Any advice would be welcome.