Simple process! Get Handbrake
, a freeware DVD ripping program. With it, and the proper settings, you can rip a DVD's main feature to your hard drive and then add the file to iTunes for sync with your iPhone. My recommended settings within Handbrake for an iPod Video/iPhone compatible mp4 video file are:
File Format: MP4 file
Codecs: AVC/H.264 Video/AAC Audio
Create chapter markers: Yes (checked)
Framerate (fps) Same as source
Encoder: x264 (h.264 iPod)
Average bitrate (kbps): 1000
Picture Settings (click the button):
Height: The height will automatically be adjusted to the correct aspect when you set the Width
All other settings in the picture settings pane are left as is (do not change them)
Audio & Subtitles:
Track 1: English (AC3) (5.1 ch)
Track 2: None
Track 1 Mix: Stereo
Sample Rate (Hz): 44.1
Bitrate (kpbs) 128
You can experiment with lower bitrates to make the file smaller. But 1,000 average makes a nice looking file that isn't too big. For instance, the movie Cars ends up as a 942 MB file with the above settings.
Please be aware that this is only legal if you are ripping a DVD that you actually own. And, of course, it would also be illegal to share the resulting file with anyone that does not also OWN the DVD.
Lastly.... Ripping a movie like this can take quite a bit of time, depending on your Mac. If your iMac is a new Core 2 Duo model then it shouldn't be too bad. Maybe an hour to an hour and a half. Slower models will take significantly longer.