Mike, your video does not show a pair of spec. Sentang spawning but it’ a video of an attempted spawning. Mostly the first embraces in a cave happen for hours without eggs appearing, especially in young pairs, but with older ones, too. This is quite normal and is called apparent pairings or sham pairings (German “Scheinpaarungen”). Every sequence of pairíngs is introduced by such sham pairing attempts, but after some time the eggs appear and the male will fertilize them. Therefore, your video is a video of a sequence of normal sham spawnings.
However, in your case subsequently there might have been no real spawnings at all. There could be two causes: firstly, the pair has no really quiet place, it’s too much disturbance around them (take the shrimps!). Secondly, there is a second male around. This is quite a bad thing for normal spawing behaviour because that is disturbed or prevented by necessary antagonistic behaviour of the two males. Therefore I think you will not be successful with this tank resp. its living community. In tanks that are really crowded by plants it might be different, but the best method is to isolate the pair in a small spawning tank without any disturbance. In nature there is disturbance, too, but with much more space, and that minimizes the disturbance.