This means video re-scaling.
Example,
1. Publish video 640x480 (4:3)
2. Play video 400x225 (16:9)
If resample_video=true, WCS will rescale video from 640x480 to 400x225 and it will be flattened vertically.
If resample_video=false, WCS will cut video to 400x225, and part of video will be lost...