First of all when shooting set your camera to have both exposures that you need, in my case, interior and exterior, properly set.

If you choose to shoot it in FullHD you will be locked to the 30fps speed, I prefere shooting in HD720 with 60fps.

As I show in the beginning of the video, Magic Lantern output a blinking video, one frame will be underexposed and the other will be overexposed. Having that in mind if you shoot in 30fps you will have 15fps of each exposure footage, and less information to bring back to the original frame rate. If you shoot in 60fps you will have 30fps for each, after the HDR merge process but you will have a finished 720p with clean frames as output playing in real time in 30 fps, instead of a fullHD 15fps that you will need to interpolate with some third-party plugin like Twixtor for AE or Chronos for Nuke.

1. Make a new comp with 720p 60fps footage.

2. Duplicate the layer.

3. Get rid of the first frame of the duplicated layer.

4. Select both layers and right-click, Time, Time Stretch.

5. Type 50 as the Stretch Factor.

6. Now you will have splited the over and the underexposed frames in different layes.

7. Duplicate the Underexposed layer and name it as Mask.

8. In the Mask layer add a Levels effect and adjust it in order to have the biggest contrast between the bright areas and the dark areas. Turn on black and white clipping with you are using 32bit comp as I did.

9. Add a Fast Blur effect and rise a lot it to have a nice transition, in my case I used 60. Check Repeat Edge Pixels.

10. Assign the Mask layer as a Track Matte for the underexposed layer. Render! The video will be played at 200% speed because your comp is set to the playback speed of 60fps.

11. Render it out as an image sequence and re-import as a 30fps footage to have ir in real time speed!

12. To get the sound of the original footage, just drop in to the new 30fps comp the original footage and hide it, leaving just the sound active.

This workflow worked great for me, but you might need to tweak some settings to match your footage and lighting conditions.

Make sure you have a clean mask to work with. I tried other ways but I think this was the most easily and effective.

Below you can watch the final result!

Hope you enjoyed! Any doubts let me know!