How did you transfer the videos? If just JPEGS have been saved, you have probably simply dragged the thumbnails from the browser onto the external volume. This way you are just saving a preview of the item and you have no control of the quality or format.
To archive photos and videos you need to select the photos and use the command "File > Export > Export unmodified originals" or "File > Export > Export ... Videos" to save the edited versions.
if you already emptied the Recently Deleted Album, the videos will have been permanently deleted. Then you can only use data recovery software to recover the items. This software is expensive and the resuts are not certain. Data recovery can try to find deleted items on the blocks on your drive, that have not yet been overwritten by new data. This can work, if you stop immediately using your Mac, so no more items will be overwritten. If you want to try this, get yourself a recovery software, that offers a trial version, so you see what can be recovered, before you have to pay for it, for exampleDisk Drill (https://www.cleverfiles.com) worked well for me, when I had to recover a deleted photo.