The easiest way to do it is to crop down to the left eye using FFMPEG.
Here is an example FFMPEG script of how to crop an SBS 3D 1080p video (with a total resolution of 3840x1080 for two 1080p videos):
ffmpeg -i filename3D.mp4 -filter:v “crop=1920:1080:0:0” filename2D.mp4
Let’s break down the important part, which is the values after “crop=”
1920:1080 is the target resolution of the output video, in horizontal:vertical resolution format.
0:0 is the coordinates of the starting point of the crop, which in FFMPEG terms 0,0 is the coordinates in X,Y of the top left corner of the frame.
So all you need to do is modify the resolution from 1920:1080 to whatever the target output of your 2D video would be, or to think of it a different way, whatever the total resolution of the SBS 3D video is with it’s horizontal resolution cut in half.
The above script will also work for Half-Width SBS, but you’ll need to perform another transform to get it to double it’s resolution horizontally after cropping the left eye.
The reason this is helpful is simple: with it, I feel comfortable shooting any video I need to shoot in 3D using my various 3D cameras and simply cropping them to 2D as needed after the fact.
Note: this isn’t nearly as useful with Leia Video Format images captured with LeiaCam, as LVF files play natively in 2D without needing any special script.
Enjoy, I hope this is useful!