AviSynth + VirtualDub2.

[nutsey]

Do you want to make side-by-side vids (like this one) with not complicated (but still very powerful) and free software?

Here is the short and quite nonintuitive guide.

1. Get and install following software:
VitrualDub2: https://sourceforge.net/projects/vdfiltermod/
Avisynth: http://avisynth.nl/index.php/Main_Page
FFMS2 plugin: https://github.com/FFMS/ffms2/releases

2. Shoot a couple of clips suitable for a side-by-side comparison. Put files into one folder. In my case I had two files named 'hdr-off.MP4' and 'hdr-on.MP4'.

3. Get ready to deal with some basic scripting.

The 1st AviSynth script (save as 01.avs, click to open with VirtualDub2):

#path to ffms2
LoadPlugin("c:\Users\user\Downloads\vdub\ffms2-2.22-msvc\x86\ffms2.dll")
#path to video files
SetWorkingDir("d:\")

#open with no audio and crop to 960x1080, use trim for sync
a = FFMS2("hdr-off.mp4").KillAudio.Trim(0,0).Crop(0,0,-960,0)
b = FFMS2("hdr-on.mp4").KillAudio.Trim(2,0).Crop(960,0,0,0)

#put crops side by side
StackHorizontal(a,b)

#overlay some text
Subtitle("HDR OFF", font="verdana", size=50, text_color=$ffff00, align=1)
Subtitle("HDR ON", font="verdana", size=50, text_color=$00ff00, align=3)
Subtitle("www.GoPrawn.com", font="verdana", size=40, text_color=$222222, align=2)

#cut to 1min
Trim(0,1800)

Save lossless output. Select 'Video-Compression...-Uncompressed RGB' and press F7.

Do the same with the 2nd script (save as 02.avs). My temp AVI files were named 'off-on.avi' and 'on-off.avi':

#path to ffms2
LoadPlugin("c:\Users\user\Downloads\vdub\ffms2-2.22-msvc\x86\ffms2.dll")
#path to video files
SetWorkingDir("d:\")

#open with no audio and crop to 960x1080, use trim for sync
a = FFMS2("hdr-off.mp4").KillAudio.Trim(0,0).Crop(960,0,0,0)
b = FFMS2("hdr-on.mp4").KillAudio.Trim(2,0).Crop(0,0,-960,0)

#put crops side by side
StackHorizontal(b,a)

#overlay some text
Subtitle("HDR OFF", font="verdana", size=50, text_color=$ffff00, align=3)
Subtitle("HDR ON", font="verdana", size=50, text_color=$00ff00, align=1)
Subtitle("www.GoPrawn.com", font="verdana", size=40, text_color=$222222, align=2)

#cut to 1min
Trim(0,1800)

Use the 3rd one to render your final cut:

#path to ffms2
LoadPlugin("c:\Users\user\Downloads\vdub\ffms2-2.22-msvc\x86\ffms2.dll")
#path to video files
SetWorkingDir("d:\")

#open 10sec clips with fade in/out
a = FFMS2("off-on.avi").Trim(0,299).FadeIn(10,$000000).FadeOut(5,$ffffff)
b = FFMS2("on-off.avi").Trim(300,599).FadeIn(3,$ffffff).FadeOut(5,$ffffff)
c = FFMS2("off-on.avi").Trim(600,899).FadeIn(3,$ffffff).FadeOut(5,$ffffff)
d = FFMS2("on-off.avi").Trim(900,1199).FadeIn(3,$ffffff).FadeOut(5,$ffffff)
e = FFMS2("off-on.avi").Trim(1200,1499).FadeIn(3,$ffffff).FadeOut(5,$ffffff)
f = FFMS2("on-off.avi").Trim(1500,1800).FadeIn(3,$ffffff).FadeOut(5,$000000)

#merge
a + b + c + d + e + f

Save with x264 codec and decent bitrate (~24Mbps would be enough for 1080p30).

[nutsey]

Side by side comparison with thumbnailed video at the corner.

This is how it's made (AVS script):

#change path to your plugin
LoadPlugin("c:\..\vdub\ffms2-2.22-msvc\x86\ffms2.dll")

#change path to your working folder with source files
SetWorkingDir("r:\")

#open stabilized 4k footage and convert it to 1080, change trim 1st 0 to cut from begining for sync
a=FFMS2("01.mp4").KillAudio.Trim(0,0).Reduceby2.ConvertToYUY2

#open 4k footage and convert it to 480x270
b=FFMS2("02.mp4").KillAudio.Trim(0,0).Reduceby2.Reduceby2.Reduceby2.ConvertToYUY2

#put b over a with 100% opacity, change trim 2nd 0 to cut total length
Return Layer(a, b, "add", x=1440, level=255).Trim(0,0)