MP4 is a digital media "container" format, not a video codec. MPEG4 is a video codec. Two different things. A MP4 file may or may not contain video in the MPEG4 codec. iTunes supports MPEG4 video, but not all video codec that might be used in a MP4 file.
You can see this link for an explanation (note: I am not necessarily recommending/suggesting the video converter being pushed by this page as I have never used it...this link just had the best explanation of the differences that I could find...so use the video converter program at your own risk...it is one of those programs that is advertised all over the place that I can never find a true independent review on...they mention a "review" by MacLife, but could not find it separately):http://www.macxdvd.com/mac-dvd-video-converter-how-to/mpeg4-vs-mp4.htm
You need to make sure that iTunes/iOS can support the video codec that is used with in the MP4 "container". It sounds like the video codec that is used in those MP4 files are is not supported by the native video player in the iOS and iTunes.
It is not "crapple's" fault that you are not using the type of video codec that they support. You would have that same type of problem Windows in terms of what video codecs that might be supported by the default video player. Actually, you would have this type of problem with any video player...if you don't use a video codec that they support, they won't play them/accept them.
You could try VLC for iOS. Then put the videos on Dropbox (or one of the other cloud services that the iOS VLC player supports) and then log into your DropBox account to then be able to download those video to the local media library of the iOS VLC player. Or you can "sync" the files to the iOS VLC player using iTunes (it will appear under the Apps tab for your iPod...scroll to the bottom of the page to see the list of apps that can sync files to the iOS device...the VLC player should be one of them). Like the Windows and Mac version of VLC, it will support way more video codec than the built-in video player.
Or, of course, you could covert MP4 file to a version that is using a video codec that the default video player can use and then iTunes will accept them and sync them.
Or you could extract the audio to MP3 as you stated. That should work too as MP3 is an audio codec and obviously one that iOS/iTunes will support (that is the format that I use for iTunes when I want to rip my CDs).
Edited by smax013, 29 July 2016 - 04:05 PM.