Hulu plus an Amazon block their content from being used with airplay. However the video app with either your own videos or iTunes video should work correctly, is this the video app that you are referring to.
If indeed airplay does not work correctly with any of your apps..
Try the following steps, check whether things are working after each step where appropriate, before trying the next.
- Check AirPlay is turned on on the Apple TV (turn it off and on if it already is)
- Check that both devices are on the same network (Settings > Wifi, on the mobile device and Settings > General > Network, on the Apple TV).
- Restart the Apple TV (Settings > General > Restart).
- Restart the Apple TV by removing ALL the cables for 30 seconds.
- Restart your router.
- Restart your mobile device.