Did you know that you can’t add a marker in the Sequencer/VSE while playing back?
No no no, you can only (dynamicaly) add them in the Timeline window.
This drove me nuts for ages! Playing along pressing “m” key madly with no result. Then creating a Timeline window and bang! Pressing “m” adds Markers in playback.
Shouldn’t I be able to add them in the VSE during live playback too!? After all I can add them from the menu and they appear after adding them in the Timeline window. Aaaargh.