From the
Wikipedia, you could find a lot about this M4V. M4V file format is a video container format developed by Apple and is very similar to the MP4 format. The primary difference is that M4V files may optionally be protected by DRM copy protection. So it can only play on your at itunes APP, if you want to play it on your Nexus 7, you should remove the DRM from the M4V at first with
iTunes Movie DRM Removal tool and then play the DRM free video on your Nexus.