The J-K-L buttons for controlling playback of video is something that comes from Avid MediaComposer. It has been copied by Apple in FinalCut Pro and Adobe Premiere Pro. Apple has got it right, Adobe only partial. I suggest that it is changed in Kdenlive to work the way it should work.

Press J once - play backwards

2 x J - backwards 2 x speed
3 x J - backwards 3 x speed
4 x J - backwards 5 x speed
5 x J - backwards 8 x speed

Press K once or as many times you want - pause. If the video is not playing, it remains in pause. It should NOT be a play/pause toggle.

Press L once - play forward

2,3,4,5 is similar to J, only forward.

Hold K pressed and press J at the same time - play backwards at 25% speed (including the sound).
Hold K pressed and press L at the same time - play forwards at 25% speed (including the sound).

There is no need in having play/pause as a toggle, as this is something most people expect to find on the spacebar. Also, pressing L will start playing, so no need to have that on K.

Thanks, I agree, and we are so close to this (except sound when not 1X), that it will be easier to make this change to the K key. Regarding that non-1X sound thing. Do you prefer that the pitch shifts or that it use some fancy DSP to adjust the speed only?

Actually, it would be tempting to go for some fancy DSP stuff here :-) But of course, this would give a hit on performance. The others just pitch things so it sounds the same way when you speed up and old analog tape machine.

I have no idea what is possible to do in this area now, but Avid can only play audio up to 3x normal speed. Higher than that is silent. Not sure if this is deliberate (is sound at 8x helpful at all?) or if it is a technical problem.

But the DSP stuff would probably make the fast speeds easier to understand.

+1

And we don't need a realy accurate sound at more thane 3x.