I have two recordings of a concert made with two different cameras, set as two separate clips on two separate tracks. I want to be able to toggle from one to the other in my project output. Is there any way to do this without having to slice up and delete parts of each track (to allow the other track to be visible) ?

No, I don't think so. You can leave one track as it is and put it on the lowest video track (V1). If you then put clips of the other video on a track above, it will bee seen instead of track V1.

Example:

V3

V2  b  b

V1 aaaaaa



Will be seen in the rendered movie as:

   abaaba

But you will have to cut your footage for track v2.

That could be done if the "transparency" effect (frei0r) would have the amount of transparency keyframable.
I guess modifying its XML effect description would be enough to achieve that?

OK, thanks for confirming that there wasn't some clever/easy way to do it. (sigh...)

Really, you ought to be able to insert anything (effect, transition) anywhere and define an arbitrary end point for it. The XML would still support it either way, right?

You should be able to do this kind of toggling by using the composite transition with keyframes with different opacities.

Hmm. That sounds promising. But I've already got something assembled, and don't want to spend any more time on it for now.

It starts here, if you're interested... http://www.youtube.com/watch?v=gWePw-S_bZI

The original DV video was transferred to a PC by my brother, dunno what software he used. I used Kino to read the DV files originally, since Kino reads the DV timecode and automatically breaks a file into individual clips when it sees a gap. Unfortunately Kino's output always garbles the audio, so then I used avidemux to slice the DV AVI file into usable clips. Then I laid out the clips in 3 video tracks plus an extra audio track using kdenlive. (2 cameras, plus a minidisc recorder fed off the audio mixing board.) After assembling I rendered it back to a DV AVI file, and used avidemux again to slice it into <15 minute chunks. Also used avidemux to transcode it to H264, for uploading to youtube.