I've been trying to use Cinelerra on and off for a couple of days. And I've had some success. I've also had a few failures as well.

First off, the 9 hour rendering mentioned in the previous article, took about 6 hours in the end. The final version was 16 minutes long. No idea why, there was no source material that long and I hadn't used that much of the timeline either. But since then I've learnt to be specific about placing the in and out points or selecting what I want to render. I also test renders on a 15 second selection rather than on the whole movie. Even a 5 minute movie will involve an hour or so of rendering at this rate, depending on hardware and effects used.

I also found that the fewer effects I used, the quicker the display would update. Common sense, especially as I come from an audio background where you can hear or sometimes even see the errors due to too many effects. For the keying, I had the following effects:
brightness/contrast -> chromakey HSV -> blur

On the movie that would become the background, I had to resize that so I used:
scale

That was it.

I found that the brightness/contrast effect made the keying worse. So I removed that. Think I was looking for a colour smoothing effect instead.

When editing, I found it easier to turn off blur and scale so that I could work with the views. The response rate with just chromakey switched on was not bad.

So I looked at the rendered file. I can see it had tried to do the rendering as I'd asked it, but the end result was wrong. It was a wash of purples and greens with very blocky pinks. If you looked closely you could the actor and the background almost as watermarks. Not good.

I tried again but on a 15 second selection, just in case I'd mistyped an option. Same problem.

I tried different video options. The one that worked best was DV. That now gives me a file I can use. However the output is still a bit blocky and I'm not sure why. I think the bitrate is high enough, but I'm just starting the learning curve there.

Some points about Cinelerra. I don't really like the user interface. There's too much opportunity to make a mistake. None of the hotkeys for menus are control-enabled, so you could potentially make a change (e.g. by pressing a single key) and not even know it.

I found the arming of tracks to be very troublesome. I'm used to some rigour and routine in arming tracks for record and editing (back from audio applications), but the way in which it is done in Cinelerra just seems to be asking for problems. For instance, to make a change to a track, you have to arm it. Ok. To make a change to several tracks, you can arm them all. There doesn't seem to be a solo function, so you can just edit whichever track you're on. So let's say you have three video tracks, each with their own 2 tracks of audio. That's 9 tracks to keep a handle on. If you make a change to the video, chances are you want the audio to follow suit. So you have to arm them as well. Want to make changes to everything, arm them all. It just gets messy. I found myself deleting from several tracks or cutting the video without the audio. It's messy because of how they're displayed on the screen. It shows 4 or 5 tracks at a time without resizing the window. That's on 1280x1024. I'm used to showing 20 tracks of audio and still having room to spare for automation effects. I think the arming concept is sound in principle but it has a flawed execution (and I admit, possibly just a flawed user in my case).

I'm tring Kino now, if you remember from it didn't work the first time. It just wouldn't process the file properly. I'm happy to admit that's probably my error about choosing the input video format. This time, I exported from iMovie as a DVPro file (probably overkill using DVPro rather than DV). And it imports fine, no conversion on import. I was about to write that there's no effect for green screen/chromakey. That's partly true, but there is a video transition labelled green screen. Hmm.

I've played with that a bit and it's not doing what I'd expect. I'll have to check the alpha channels and look further. Also only seems to be doing anything vaguely correct on the lower half of the screen, the top half is completely wrong. Maybe an aliasing issue. Even importing DV rather than DVPro and there were issues on import.