I don’t think that macrumors post is correct: AVC ist just a name for H.264, see Wikipedia.
A common issue with ffmpeg encoded videos is the pixel format: Why won't video from ffmpeg show in QuickTime, iMovie or quick preview? - Ask Different . However, with your settings VideoIO should use yuv420p which should work in QuickTime so it would be good to have more information:
What is your VideoIO version?
Can you show the output running ffprobe video.mp4 in the terminal?