So without paying $4K for a professional license a method I've found useful is to fly with the camera pointing directly down. Can take video or plan waypoints and snap stills. Either work. I've taken the 1080p video, paused it and grabbed the frame which to me is nice because I can grab the perfect overlap in post-processing. Once you have the still you like, you can use Google Earth and do the following.
Click image overlay, add in your DJI still created as a native still or from the video.
Size it and match up with recognizable features (requires you to know where the picture was taken).
When happy with the alignment click 'OK'. You can use the slide scale of opaque to see a transparent view of the overlay to match it up.
Using Google Earth as your geo-anchor, you can create an orthomosaic of 2D images that are saved then as KMZ files. To save them as KMZ files you can right click on the overlay and choose Save As.
Some things I've come across that create this manual tie process intensive. The DJI Phantom 2 Vision + and likely GoPro skew the images on the edges making geo-rectification difficult. Typically I throw the image in PowerPoint or Preview and crop out about half the raw image to make a square. It's sorta an art depending on your 'look' angle but I'm sure there's an easy way to do it.
Last, you can always use a free Android app called Custom Maps that allows you to take any .JPG, etc. and tie to Google Earth with the output file of a KMZ file - an easier interface than Google Earth and mobile which is nice when you don't want to lug a laptop with you. Overall, I hope in the next year to find a video mosaic tool that doesn't cost an arm and a leg.