Many thanks again for the idea Jeremy. Unfortunately the “jump cut at markers” gives a strange effect in these circumstances as it doesn’t leave physical cuts where I can insert Cross Dissolves. Those are vital for me.
In the end I did the following which I’m writing out in detail in case it could help some other relatively inexperienced user:
1) Select the clip and position the CTI at the END of the clip
2) Press J (maybe twice to speed things up) for a ‘longish’ clip of say 15 or more seconds. (‘Longish’ clips are those that will be deleted at the end of the process). Press the spacebar to stop the CTI and then press Cmd-B
3) Press J and leave for about three seconds, press the spacebar and then press Cmd-B. This gives a ‘shortish’ clip. All the ‘shortish’ clips will be kept and cut to the same duration in 6)
Repeat 2) and 3) until the beginning of the original clip is reached.
4) Using the Cmd key, select all ‘longish’ clips one by one and delete them
5) Select all remaining clips, ie. the ‘shortish’ clips
6) Ctrl-D and enter, say, 200 to make all remaining clips 2 seconds long
7) Leaving all the clips selected, double click on Cross Dissolve.
I was really lucky and the resulting length gave me just about what I had in mind. I made a minor adjustment to the music length. overlaid my scrolling ’Credits’ title and at least my wife is really impressed!
FCPX and PPro 6. iMac 24 + MBP 15″. Near Geneva, Switzerland