My Itunes dont synch m4v movies to my Ipad, Error message say It cant be played on Ipad. I find that strange since it plays perfectly in Itunes.
Anyone knows why ?

I had a similar problem, although I didn't get the error message.

You need to check that the file is the correct format. iTunes on your PC will still play it but won't but it on the iPad if the format is wrong.

Sound nice

The reason could be that the sampling rate of the sound is too high. Use MPEG Streamclip to convert your movie to the right size and sampling rate. You can find the settings here.

I think you should remove DRM from your purchased or rental M4V file and remove DRM protection from popular video and audio files, Maybe beacuse of the different format .
You can use a M4V Converter , it can helps you remove DRM .