Hi xopox,
Looking at this, I’d recommend replacing your embed codes with a one-line video embed for each video. This is where you place the video URL on it’s own line in the content, and WordPress embeds the video for you.
A filter on the_content would be a good way to start, with a regex to match all div tags with the video CSS class. From there, pulling the URL of the video out of the matched text, and replacing the div tag with the video URL, would achieve the desired result.
This would also be non-destructive, as it doesn’t actually replace the content in the database, yet overrides the videos with new embeds.
I hope this helps, as a starting point.