Several ways of doing this.I have a question, though. How do you get sound on your video? I assume the mic must not be on the drone, or there would have been prop noise.
One, make up a sound track and add it.
Two, set your App to record sound along with the low res video it records and use that video. I think this is what the OP did as the video is 720p
Three, same as 2, except use the high res from the SD card and sync the sound track from the App recording to it.