IPhone - view video in the application

You can use UIImagePickerController:

Example:

UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.delegate = self;
picker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
[self presentModalViewController:picker animated: YES];

Remember to implement the delegate protocol.

Here is a link to Apple docs: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIImagePickerController_Class/UIImagePickerController/UIImagePickerController.html