I'm looking for a video player that builds a playlist from the folder when I open one video file. Ideally, opening a numbered episode would add the other playable videos from that directory in the correct natural order, so files such as ep_1.mp4, ep_2.mp4, and ep_10.mp4 don't get sorted alphabetically as ep_1, ep_10, ep_2. It would also be useful if dragging a folder into the player or opening the folder directly produced the same playlist.
3 Answers
Some desktop environments or file managers can provide an “Add to playlist” action for folders, but that option may depend on the player and desktop setup. If opening one file doesn’t automatically include its neighbors, opening or dragging the whole folder is usually the more reliable approach.
Haruna appears to do exactly this. Open a video from a folder and it adds the other videos in that directory to the playlist panel. It also seems to use natural numeric sorting, so unpadded episode names are arranged as ep_1, ep_2, ep_3, and then ep_10.
mpv can add an entire directory to its playlist when you pass the folder path instead of an individual file. For example, running `mpv /path/to/folder/` loads the playable files and starts with the first one. Most players also let you add the folder directly to the playlist, even if they don’t automatically scan the folder when a single file is opened.

That makes sense. I mainly wanted automatic queueing when launching an individual episode, but adding the folder works as a fallback if the player doesn’t support that behavior.