Some MP4 H.264/AAC files without sound - Found a fix

I was just about to describe the issue below I was having for years now. Then I had an idea, tried it — and it actually helped: simply changing the extension for all files from .mp4 to m4v!

I had tried something before via VLC, where you can "convert" the audio track to MPEG4 audio (AAC) (which I thought it had before) and the result of this was a .m4v file, which actually played the audio in iMovie again. However, since manually converting audio tracks for all the problematic video files would have been a huge task, I didn't proceed with that.

While writing the following post, I suddenly thought that simply changing the file extension to .m4v could be worth a shot in the dark :D

This is the issue I had:

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I have a collection of mp4 clips, which all have been created via the same Handbrake profile. However, some of them don't have any sound when importing them into iMovie. The Audio plays fine in QuickLook or the QuickTimePlayer app. Again, some files play the audio fine and they should all be the same regarding codec settings.

Interestingly, this worked well in iMovie until a few years ago, when an update was released. I have been hoping since another update would fix it.

All clips have, as mentioned above, H.264 (mp4) video and AAC audio.

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I hope this helps other people having the same issue!