you need to make sure that the format is correct to move over to the phone click on the video to select it in the movie list in itunes, then click the advanced tab on the toolbar on top (beside file edit tools help ...ect.), go down to the option that says "make iphone compatible/version" (it may say something different but it will sound something like that). click this and let itunes convert. Then after it finishes try syncing again.
Secondly depending on what firmware the iphone is running on it could be a problem in the transfer method. To solve this issue you can check manually manage videos and music on the iphone mainscreen and then drag the video over to the iphone. I personally like this method of syncing better because it gives you more control and you can sync across more than one library easily. |