user26248: Based on the answer to this question, how would the command line
ffmpeg -i input.mp4 \
-filter_complex "[0:v]crop=in_w/2:in_h:0:0 [top]; \ 
[0:v]crop=in_w/2:in_h:in_w/2:0[bottom]; \
[top][bottom]vstack[outv]" \
-map "[outv]" -map 0:a -c:a copy output_3dv.mp4

be changed to do the opposite, split two stacked images (3240x2160) to one 6840x1080 video?

user1871: You would crop the full width and half-height. Then use hstack to join them.
ffmpeg -i input.mp4 \
-filter_complex "[0:v]crop=iw:ih/2:0:0 [left]; \
[0:v]crop=iw:ih/2:0:ih/2[right]; \
[left][right]hstack[outv]" \
-map "[outv]" -map 0:a -c:a copy output_3dv.mp4


26248: <p>Based on the answer to <a href="https://video.stackexchange.com/questions/17131/convert-horizontal-side-by-side-to-vertically-stacked-3d-video?newreg=5ad754b5b60d46fc80546d15fb66b35c">this question</a>, how would the command line</p>

<pre><code>ffmpeg -i input.mp4 \
-filter_complex "[0:v]crop=in_w/2:in_h:0:0 [top]; \ 
[0:v]crop=in_w/2:in_h:in_w/2:0[bottom]; \
[top][bottom]vstack[outv]" \
-map "[outv]" -map 0:a -c:a copy output_3dv.mp4
</code></pre>

<p>be changed to do the opposite, split two stacked images (3240x2160) to one 6840x1080 video?</p>
 1871: <p>You would crop the full width and half-height. Then use hstack to join them.</p>

<pre><code>ffmpeg -i input.mp4 \
-filter_complex "[0:v]crop=iw:ih/2:0:0 [left]; \
[0:v]crop=iw:ih/2:0:ih/2[right]; \
[left][right]hstack[outv]" \
-map "[outv]" -map 0:a -c:a copy output_3dv.mp4
</code></pre>
