Q: How to sync videos from computer to iphone

You can sync Movies and TV shows through iTunes. Just sync them automatically using the Movies and TV Shows tabs, or drag and drop them onto the iPhone by manually managing the iPhone.

iOS: Syncing with iTunes

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You might have to Create a iPod or iPhone Version of videos, if you didn't download them with iTunes.

before you sync you need to make sure that your videos are MP4 format not "avi" format. in case they were "avi" you can simply covert them into mp4 using iSquint. once they are converted, you can drag them into itunes and sync using movies and TV shows tabs.

You can download the free iSquint to convert a video for iPod/iPhone use.  Once converted, the video can be synced and transfered from iTunes to your mobile device.  Video will be added to the Video App.  Hope this helps.  Next question for me is how to share the video using Viber because it cannot be retrieved from the "Gallery." (sigh)

That's fine with movies and TV shows... but what about previous videos shot on the iPhone?? I can't, for the life of me, figure out how to transfer videos from my computer back to my iPhone. Do they show up in Photos or Videos app??

Same question here.