You will want to set the H.264 level of those videos to 4.1 at most; then, iTunes will be able to synch it. Use Subler for this. Here's my quick tutorial:
In Subler, click the video track in the upper list if you want to play the video back in the stock
Videos app on your iDevice and not in a third-party one. (iTunes refuses synchronizing anything over level 4.1.) If you see anything larger than 4.1 (4.2, 5.1 etc.) in the bottommost
H.264 Video Profile / Level drop-down list, feel free to set it to 3.1 or 4.1 to enable synchronization:
Image
(Make sure you select the video stream and nothing else for the drop-down list (annotated by a red rectangle above) to become visible AND editable! It'll be the uppermost item, as you can also see in the above screenshot.)
Again, this can be done to already-existing M4V files which have too large a level to be successfully synchronized by iTunes to your iDevice. Actually, using Subler to patch an existing over-leveled m4v file is much-MUCH faster and more reliable than the traditional, old ways explained in
my dedicated article.