mp4 not playing on MacBook
My macBook MacOS Sequoia won't play my mp4 files. My old Big Mac plays it.
MacBook Pro 13″, macOS 15.1
MP4 may be the greater overarching video format that manages many different styles of video. Sadly subcomponents of MP4 known as Codecs frequently become obsolete meaning you have to convert them to a current Codec on the old Mac to be usable on the new Mac.
Indeo video Codec is a big one that no longer is supported. Some videos may be copy protected, and you may need to transfer an Apple iTunes Store account to the new machine for the MP4 to be playable on your new Mac, if it uses the same AppleID. You are limited a number of computers per AppleID and you can get the iTunes store account to forget older computers if you have reached the limit.
AVI for non-copy protected videos sometimes requires a Divx plugin to support those videos, or one from Windows Media Player. You can run Windows on the Mac for moving copy protected videos from a Windows machine to a Mac, as long as only maintain the number of copies you licensed yourself for them.
Running Windows on a Mac, and Connecting … - Apple Community