Were you looking for a guide on how to for videos, or are you troubleshooting a Synology NAS setup?
Because the DS hardware isn't fast enough to decode modern H.264 or H.265 MP4 files, you cannot simply drag an .mp4 onto an SD card and hit play. You must convert the files into a format the DS can handle, typically (a specialized MPEG-1 derivative). What You Need A Flashcart: Usually an R4 Card or similar. DS.mp4
Users often compare DS Video to Plex, noting that Plex sometimes offers smoother playback for high-resolution files. Were you looking for a guide on how