I have an iPhone 3GS with iOS 6 an I would like to watch movies on the TV, therefore I bought an AV composite cable. Only videos that are located in the "photos/videos app" can be played on the TV through the AV cable. Is there an app that can download videos from YouTube to that folder?
It's always a bit tricky to download anything on iOS devices..
When I want to download a youtube video I open the YouTube video in my browser and add "dlv" in front of youtube so that it reads www.dlvyoutube.com and there download it.. Then I transfer it over to the device with iTunes.
The only means that I know of, is to jailbreak your iPhone. you would need use applications available for Windows, Mac, and Linux, such as Evasi0n. The first and most important thing to do is to make a complete backup of your phone in iTunes. Secondly, you must download Evasi0n for your platform of choice, open the application, and plug your device in via USB. When the program has successfully completed, you should find a new app on your iPhone called Cydia. From here you can download the tweak YourTube. this app is an extension of YouTube that allows you to download any video for free.