Can I change .MOV files to .MP4 just by changing the extension? Would that potentially cause any problems?

Well since I am an A/V expert and have worked with about a million A/V files over the years,

Changing the file extension does nothing. Since you changed from one to another video extension is the only reason the video plays. It is still a MOV file. You can not change a file by its file extension. It has to be encoded or ripped to a different format. There are many variables when ripping files too.

You can use many programs to encode them to mp4.

AVS and AVC video converter programs are about the best. AVS is better for editing out unwanted sections.

For creating 4K HEVC H.265 formats, you will need to look around for a free ripper or purchase one.

BE CAREFUL WITH FREE PROGRAMS AS MOST ARE LOADED WITH MALWARE LIKE THE ADVICE YOU WERE GIVEN EARLIER AND THE THE POSTER DELETED HIS COMMENT.

As for playing them, you can play pretty much all video and audio formats in Windows Media Player using Shark007 advanced codec pack. Including 4K, DVD and Blurray. Also nice thumbnail previews. Free no malware and never have any issues.

Install sharkk007, close out 64bit settings app.

in 32bit settings app, select shark007 suggested settings and close out.

Select WMP as default player for audio and video files.

https://answers.microsoft.com/en-us/windows/forum/windows_other-pictures/wmp-play-all-video-audio-formats-easily/ae900cb4-2e8e-4cca-aadb-8da60b1c1464

I have used shark since Windows XP on all OS's. it is the best codec pack in the world.

1.) They obviously aren't that different because I've done it several times thus far.

2.) I'm not talking about AVI.

and 3.) Wtf are you recommending, you fool?

https://www.virustotal.com/#/file/4f84bbca18f76d5464b5738f74197dbd320d4d40d09f92536c72e8d476b515e2/detection

No, you cannot simply change the extension. However, it's easy to convert .mov to .mp4.

Simply use this as the search term in your favorite search engine:

convert .mov to .mp4

Thanks for the response.

I prefer to use Media Player Classic Home Cinema with Combined Community Codec Pack. Been using that combo for years and have been able to play any video file I've encountered.

Being an A/V expert, are you aware of any encoders that will be able to convert H.264 videos to H.265 while retaining all of the metadata on the files?

That's mainly why I did not want to re-encode, every encoder I've tried removes at least some of the metadata, which is important in this case.