Black lines in video - FYI - solution found - this is an mp4 issue (not a Storyline problem)

>Please note, that is it possible to crop a video in Storyline that will result in black bars where >there were none before.

I have seen that on other video compression tools for mp4 (Adobe Media Encoder, ...) - the reason is the limition of mp4 with width and height (-> jpg compression artefacts on the right und bottom site for p-frames)

https://en.wikipedia.org/wiki/JPEG#Block_splitting

Block splitting: the best image size is
 - width is multiple of 8
 - heigh is multiple of 8

for all other sizes - the compressor has fill the incomplete blocks with color info for the following math (DCT) - and crops it at the last (???) step

(thats for b/w, for color is more complicated)

=> result 1: create your storyline layout so, that the video sizes are a multiple of 8

=> result 2: set videos in storyline to "no compress" (compress the video with special tools [ffmpeg, ...] with special settings and test every video individually before import to storyline)

mp4, h264 is designed/optimized for 16:9 with fixed sizes (128x96 ... 4096x2160)

https://de.wikipedia.org/wiki/H.264

subsequent cropping is never a good idea overall - no matter for which losy medium (mp3, mp4, jpg, gif, ...) - the only exceptions are lossless wav, flac, png, ...

Jürgen