I have had this problem for a very long time, had several discussions with friends, and tried searching relating info online. All efforts were in vain so I decide to give a shot here.
I have lots of files that I would like to annotate. Not necessarily are they pictures or documents, but also audio/video files. Now, I understand that there are ways to annotate a PDF, and there are ways to add metadata to PDF/mp3/mp4.., but those methods are not enough for me.
More specifically, when it comes to PDF files, usually I would like to take some notes in my favorite format. The current best way I can think of is to create another file with the same name and put them in the same directory (or tar them together), e.g.
Learn-How-to-Learn.pdf.note.md. However, I found this method cumbersome, for instance it is hard to always link them together and with their names synced.
When it comes to mp3/mp4 files, I also want to link them to other files that contain my notes. For example,
00:45:37,I would like to listen to this part again,20190610T19:03:56 01:03:55,Donald Knuth made a good point on blah blah,20190610T20:00:03
These examples go on and on.. I feel that this is very useful, and there must be some clever solutions out there. But to my surprise, I haven't found any! Please let me know if I should be clearer.. sincerely I would like to have a beautiful solution. Thank you in advance!