Hi Everyone, I have been experiencing the same issue with the Photos app Store, I would be missing about 10,000 pictures and then they would appear again. This has happen a couple of times since I switched from iPhotos to Photos app, its been a few years. Over the last few days it happen again and ever since then I've tried and tried to recover my precious valuable photos but had not luck, until this morning. I HAVE RECOVERED ALL OF MY 10,000 PHOTOS! what i did was
1. open finder
2. go to pictures
3. scrolled all the way down until I found a folder labeled "A Day at the Museum" and another one labeled "Photos Library
4. I doubled clicked on the "Photos Library" and Photos app opened up and a small window pop up asking me if i wanted to switch from " a day at the museum" to "photos library". I clicked yes, although I was terrified of loosing the remaining photos, and after it made the switch and Photos app re open all of my pictures appeared. Hope this is helpful, best of luck. Let me know if it worked for you guys.
Safari reads MP4 formats differently to every other browser out there, hence the reason why they don't display.
There are various discussions about it out there and various changes suggested to the way servers are configured in order to resolve it. However, any changes will have other impacts and tbh there aren't many people who use Safari and then you've got to factor in how many want to view the videos in mp4 format, before evaluating if the changes are necessary.
In addition we don't have any control over the servers that videos are stored on if the video is only included by linking.