Kdenlive Timeline Illustrated, Part 2

In my second blog post about Kdenlive's timeline we now learn how to find the topmost track that gets rendered as well as where the «rendering pipeline» of tracks chained by transition actually ends. In case your haven't yet read my first blog post of this mini series, Kdenlive Timeline Illustrated, Part 1, then please read it first as it sets the context to understand this second post.

Update: added link to part 2 of this mini blog post series.

Where's the Beginning of the End?

So far, we talked in detail about how clip effects are applied to clips only but never transitions, and we saw how transitions can be chained and the order of track compositing basically reversed. But at which track and clip does Kdenlive (or rather MLT, multimedia framework) start? And where does it stop?

So I've drawn up another illustration...

Rendering illustrated in Kdenlive's timeline.

Again, we are looking at an example where the chain of transitions ends on an empty track. I have to admit that this is by far the most-seen case in my projects.
  • To find the start, look for the topmost clip on the timeline (as usual, at a specific timecode position). In my illustration above, this is some clip (1) on track 2.
  • Hunt down the chain of transitions (2) until...
  • ...until you arrive at a final result (3). That is, a result from which no further transition departs. In our case this the empty track 5 to which the transition on track 4 chains to.
  • The project result (4) now is the compositing of all clips that are chained to this result either directly or indirectly.
Please note that the clip (5) on track 6 gets ignored and doesn't get into the project result at all. The reason is that no transition chains to it.

If you wonder what happens to the other clips, in particular, the one on track 3: it gets also into the compositing process. It gets picked up as part of what I call backtracking (6). Starting from the final result we go back transition by transition (that is, finding WITH properties that point to us) until we reach a dead end, erm, dead start. Of course, we might see branches as we backtrack.

The Timeline Tree

And backtracking already hints at that Kdenlive's timeline is no simple layering mechanism as it is known from so many graphics programs. Instead, the transitions combine tracks (or rather clips) in a tree-like fashion. Well, let's just illustrate this...

It's a Timeline ... tree!

Since multiple transitions can simultaneously reference the same other track using their WITH properties, we have branches. The consequence is that Kdenlive's timeline represents rendering or compositing trees. Unfortunately, this does not exactly become clear from the metaphors of the user interface.

To me, it is sometimes not easy to figure out how to set up the tree correctly in form of transitions and on which tracks to place what. In such situations I would like to have a flow-like compositing view instead for selected areas of the timeline. But at least with the explanations above and the illustrations it should now be easier to come up with the required tracks and transitions in many cases.


Hopefully, you have gained a better understanding of how Kdenline's timeline works. In the my third blog post I'll finally show real-world examples.