[sysoverload]

I wrote my own chapters for something that I had converted to mkv once. I just used a media player's seek bar, and wrote down the time that each new song started, then wrote out the chapters and times to a text file in the right format, and added it to mkvmerge.

I would think it would be similar for mp4. you just have to write it using the correct format. use one of the mp4box GUIs, like yamb, to demux your M4Vs, then edit the chapter text file to your liking, then remux. I don't know what the mac equivalent to yamb would be.