How to sync videos from computer to iphone 4?

I have videos that I took with my friend's phone and I uploaded the videos and the pictures onto my computer. I'm now trying to sync the videos from my computer to my iphone 4. I synced the pictures but the videos will not sync for whatever the reason may be. When I select the album with the videos it says there's 0 anything. What is the problem because I really want to get these videos onto my iphone 4 but itunes won't let me sync them onto it. It let me sync the pictures but not the videos. What is the problem?

Change phone

I gather you have enabled video sync in itunes, right?
Because you have synced pictures, it does not mean that videos will be copied as well. Separate Tab for that.

What extension do these videos carry? (AVI, MP4, MOV.)

1. Turn off the automatic syncing feature on your iPhone if you do not want everything in your iTunes library on your computer to be added automatically to the iPhone without asking you first. This is an especially good idea if you will be connecting your iPhone to more than 1 computer on a regular basis, because it will prevent you from accidentally overwriting files from your primary computer. To prevent auto-syncing, you must first connect your iPhone to the computer with the USB connector that comes with your iPhone.
2. Select your iPhone from the device list within the side panel of the iTunes library after iTunes opens, which should happen automatically anytime you connect your iPhone. Click on the tab labeled "Summary" and uncheck the "Automatically sync when this iPhone is connected" button if it is checked. If it is not already checked, then your iPhone is already set to prevent auto-syncing and in either case, you will still be able to sync your iPhone manually by clicking on the button labeled "Sync."
3. Use the tabs in the iTunes side panel to choose the types of media playlists you would like to sync between your computer and iPhone. The iPhone allows you to transfer playlists of music, videos, podcasts and audiobooks. It is important to note that only 1 type of media can be included on each playlist.
4. Allow iTunes to create a special playlist automatically if you have more music on your computer than will fit on your iPhone. If your iPhone has reached its storage limit, a message from iTunes will pop up and ask you if you would the program to create a playlist full of random songs from your library, which will then automatically sync to your iPhone. You can customize the random playlist by adding or deleting songs of your choice and then simply syncing it again with your iPhone by pressing the "Sync" button in iTunes.
5. Keep in mind that you can only sync playlists from your computer with 1 iPhone at a time. Always make sure to be logged into your own Apple account when updating your iPhone and remember to disconnect one iPhone before adding a new one. Failure to do so may cause your iPhone to sync incorrectly, possibly erasing content from your iPhone.

Itunes

Set up a free Dropbox account…

http://db.tt/X81uh87

and use the free Dropbox app on the iPhone to pass the files between the computer and phone…

https://itunes.apple.com/...30330?mt=8

Maybe itunes doesn't support the format of video. Find a program to convert it first, then transfer it to iphone. I met similar problem before then solve it through xilisoft ipad magic platinum. You can download it to have a try.http://www.xilisoft.com