Swapping video sides of side-by-side clip with ffmpeg At the moment i am using handbreak to encode gaming clips made with Fraps while using 3D Vision by Nvidia. It is the only recording app to produce 3840x1080 Full SBS when recording using 3d Display with 1080p.
Sadly the right side is displayed left, and youtube won't allow swapping sides in the settings, only in flash version of youtube the toggle exists. 
Using ffmpeg to encode my clips, is it possible to use a command of crop and stack to produce the output? 
Option desired are: h.254, PAR width:height=1:2, constant quality: rf=17, framerate same as source
There may be an easy, quick way out, which is to remux to Matroska and set metadata to indicate that the right view is on the left.

ffmpeg -i in.mp4 -c copy -stereo_mode right_left out.mkv


Upload to Youtube and check.



Else, FFmpeg has a filter to handle this directly.

ffmpeg -i in.mp4 -vf stereo3d=sbsr:sbsl -crf 17 -c:a copy out.mp4


The filter interprets the input as side-by-side with right eye view on left side (sbsr) and swaps the halves.