Trying to burn five .m4v files to a disk image using iDVD 7.1.2

But within about minute I get the "there was an error during movie encoding" message. I've tried multiple times and changed to a less demanding theme but still get the same error. I haven't tried burning directly to a DVD since I presumed the 'disk image' route was simpler and safer.

The files were originally on DVDs and I used Handbrake to convert them to .m4v files to burn a DVD using iDVD. The files play fine in Quicktime Player. I'm using a 2013 iMac running Yosemite 10.10.5. I even tried burning the same files on another iMac running 10.10.4 but got the same error message almost immediately the process began.

I'm guessing it's something about the Handbrake x264 encoded files, but don't have enough tech knowledge to figure out what it could be or how I might solve the problem.

Has anyone had the same problems or know of a solution?

Thanks!