Edit your Windows Phone 8.1 videos with Video Tuner
The app offers dynamic changes, which means that when you add or change an effect, you can see it applied to your video immediately. And using the music library on your phone, you can add songs to the background, or raise the volume of the sounds you recorded with the video. While you can't upload directly to Vine or Instagram from the app, you can save your finished work of art and send it via email or as a text message. Once you save it on your device, then you can upload it to a social network.
Video Tuner is a free app, available only for Windows Phone 8.1 powered handsets, and weighs in at 40MB. If you fancy yourself as the next Spielberg, you are going to want to use Video Tuner to complete your latest video.
source: VideoTuner via WPCentral