To be honest, I have no idea about how to remove DRM from iTunes videos
in common way. Now there are third party DRM removal software can help us get rip of DRM protection and convert videos from M4V to MP4 at faster speed with zero loss quality. Media Converter for Windows is my option. I have used it to convert iTunes videos with all audio tracks, subtitles including AC3, 5.1 Dolby surround audio, cc, etc. Now there is a Christmas discount sales of this tool, click here
to check more info. Good luck.