I can handle lsnes movies. :)
Speaking of the lsnes movie editor, it's a bit hard to use it properly if you don't know how to select multiple frames and using branches and use savestates.
The first thing I recommend to do is "Change number of lines visible" and deactivate "Lock scroll to playback".
Selecting multiple frames: Right click on the first frame you want to select and hold the right mouse button, then draw over the frames you want to select, release the right mouse button and select copy/cut/delete(/toggle input/clear input - in case you selected individual controllers).
Using branches: When you make a new branch it will copy the current input to the new branch. When you're modifiyng inputs on the new branch it will not affect the old one. Branches look like this:
---------
|Branch1|
/---------
------- /
|Start|
------- \
\---------
|Branch2|
---------
When you're trying to switch to Branch 2 while you're in Branch 1, you can get this message "Can't change branch: Branch '1' differs in past." You can still easily switch branches by going back to the beginning of your movie: Movie -> Rewind to start.
Using savestates: Savestates in read-only mode work different than in read+write mode.
You can easily mess up your work! Never switch to read+write mode if you don't have a savestate or branch with the entire input file you already made. If you switch to read+write mode the inputs after the current frame are lost.
In case you need to switch to read+write mode, because you get this message "Can't load movie/savestate: Save is not from this movie", you should first save the inputs to a savestate, which you shouldn't use while actual TASing, or save the inputs to a new branch.
Quick frame append With a left mouse click on the frame counter you can append a frame. By holding down the mouse button and drawing over frames, you will append the number of frames you selected. Altough this feature is not really needed, but nice to know
There might be more featuers like that, I don't know if there's an instruction manual of the movie editor, these are just things I found while TASing.