How to use the composite transition to layer multiple videos and image files together.



I searched the forums looking for how to do this and didn't come up with anything. I finally worked it out myself, so thought I'd post something in case anyone else has this problem.

I am working on some training videos, have done a rough cut, and want to overlay a talking head, explaining what is going on. I found that this was fairly straight-forward if my overlay was over a single clip, but often, I want the talking head to continue over several clips that are edited together, usually with a dissolve or other transition between them.

In the composite settings, I found that if I used the default "auto" in the "with track" drop-down, everything would work fine until it hit the transition between the two base clips, when, of course, my overlay would disappear as the new clip dissolved in.

I tried several things, and found myself drowning in a chain of composites with each track overlaying the one below. It nearly seemed to work sometimes, but if I sneezed, everything would fall apart, and behave erratically. At one point I was seriously thinking of rendering my base clips as a lossless video and overlaying my talking head over that, but that would have been cumbersome, especially if I need to re-edit (which I fully expect).

SOLUTION:

Then I noticed the "Black" option at the bottom of the "with track" drop-down. A quick bit of googling revealed that this is a hidden track at the bottom of the stack.

So I tried compositing ALL tracks (i.e. include the base tracks) onto the hidden "Black" track. And everything works as expected!

One problem, because composite is a transition rather than video effect, is that I had to replace my original transitions between base clips, but the composite transition itself has keyframeable transparency and wipes, so I was able to recreate everything. If you wanted slides, or other transitions between base clips, I'm not sure if it would be possible.

To give an idea of what is possible, the sample video above consists of:

1. A .png image - the bright yellow frame around the talking head.

2. The video of the talking head, which has Scale0tilt and Blue Screen effects on it. The Scale0tilt to place the head in the frame, and Blue Screen because I want a specific colour for the background.

3. A pastel yellow colour clip for the head to sit on. I copied the Scale0tilt effect from the head video onto it, so it sits in the same space, inside the .png frame.

4-6. Three base clips for all that lot to sit on. There is a dissolve transition between the first two, and a clock transition between the 2nd and 3rd.

Each of these clips has a composite "transition" and each "with track" is set to "Black". At first I thought I would have to have the talking head track compositing onto the colour clip, since I am using chroma-key, but that is not the case, and in fact the set up seems much more stable with everything compositing onto the invisible Black clip.

I hope this helps someone.

PS: I do realise the chroma-key is a bit rough but this was only an experiment after all!

Thailandian, thanks for posting this.

I am relatively new to kdenlive, so I played around with this and got it working, but it also got me thinking that there could be a less cumbersome way to achieve this. It appears that the only way to attach an alpha channel to a track is by using the composite transition, which then composites with a specific track or black. This is a bit cumbersome for two reasons - one, because the composite transition must be applied to every track and set to composite to black, which initially isn't very intuitive, and two, because it precludes the use of other transitions, such as slides.

Instead, why not have each track have a built-in alpha channel that is aways present and not tied to a specific other layer as a transition is. In that case the multi-layer composite can be acheived by simply making part of a higher track transparent and it would automatically composite in the expected way over the various lower tracks. Before moving to kdenlive, I used Cinelerra, which works this way and makes this sort of multi-layer compositing very easy and intuitive. This paradigm is also used in tools like Gimp and Photoshop, which makes it more intuitive for many people.

Incidentally, playing around with this also led me to the somewhat non-intuitive epiphany that the "transparency" effect also requires the presence of a composite transition to work (in order to get the alpha channel), so now I know how to use that as well :)

Dave

Thanks Drosky for shedding a bit of light on what is happening. I had a similar experience with chroma-key - set up the effect, but couldn't get it to work until I put a composite "transition" on it.

However, I disagree about having alpha channels per track. I can't think of an example off-hand, but I can imagine there would be instances where you would want alpha on some clips but not others on the same track.

Rather than that, would it be possible to make an alpha channel effect? Using a "transition" for a whole clip to get alpha is counter-intuitive.

BTW I also used to use Cinelerra, but have pretty much switched completely to Kdenlive, and mostly because the UI _is_ more intuitive. At least issues like this are the exception with Kdenlive, and there is a clear impetus to make it accessible.

It would be fine to have only some layers have an alpha channel if that makes sense in some cases, although if every later had one, you could simply set it to be opaque for channels that you don't want to have transparency.

The main point I was trying to make is that the steps Kdenlive requires you take to achieve this type of compositing is not very intuitive when viewed in light of how just about every other tool works, and it imposes some limitations that are difficult and/or complex to work around.

I agree that Kdenlive has evolved to the point where it is preferable to Cinelerra for most projects that I do. It has evolved to the point where there are now some things that each tool can do that the other cannot easily do. There are still some projects that I use Cinelerra for, particularly if they require complex keyframing of effects that can't be done in Kdenlive (virtually everything can be keyframed in Cinelerra), or if they require complex, keyframed manipulation of 5.1 sound track panning and such (Cinelerra has some sound editing capabilities that many commercial NLE's don't have). OTOH, there are certain transition+effect combinations that are possible in kdenlive that are not easy to do in Cinelerra, for example, having a Ken Burns effect occurring during a wipe or slide transition.

There are cases where I use both. I have one recent project where I edited the video in Kdenlive, and then brought the rendered video into Cinelerra because I had some complex panning of sound channels to do that was much easier to do there.

Dave

THANK YOU!!!! I can't believe I found this so easily!! This needs to be more accessible i.e. putting it in the kdenlive transitions page (https://kdenlive.org/project/kdenlive-transitions/)