How to Play, Convert YouTube to iPhone 4 on Mac
This article is going to demonstrate how to view YouTube videos on iPhone 4 with a Mac. Note, if you are Windows user, please go to YouTube for iPhone 4.
Since most downloaded YouTube videos are FLV files which are not friendly with iPhone 4 and therefore can't be play on iPhone 4. To play YouTube on iPhone 4, you have to convert YouTube to iPhone 4 videos like MP4, M4V that can be easily work with iPhone 4. What you need is iPhone Video Converter for Mac. Now, I will take you to the guide on how to use iPhone video converter to convert YouTube videos to iPhone 4.
Step 1 Download and open 4Videosoft iPhone Video Converter for Mac. Download Link

Step 2 Click "Add File" to import YouTube videos to the program.
Step 3 Set the output format at "Profile".
Set the output destination at "Destination" for the converted files. You can either choose MP4 or M4V.
Step 4 Start converting by hitting the blue button of "Start".