I think related to #65 (which I super appreciate btw!). When I download a video via browser or yt-dlp, it saves with a jpg extension automatically instead of mp4.
https://bibliogram.art/p/CgkSf0DgJAI an example video
Thanks for the detailed report! Should be fixed in 1872391a8ea1d5341f35e9458d98bf4d2b155d91, which is now live on bibliogram.art.