Q I have some old iMovie files that the current release of iMovie seems unable to open. Has it lost backward compatibility, and if so, how can I convert them?
A If your old iMovie projects were saved by version 5 (the first HD release) or earlier, then there are likely to be problems trying to open those projects with newer versions.
You might be able to work around this if you have updated copies of the intermediate releases of iMovie, as you are more likely to be able to open a version 6.x project using iMovie 7.x, and so on. You could then save a series of intermediate conversions, until you finally get to one saved by iMovie 8.x, which should work fine with the current version 10.0.9. However that is laborious and requires old versions of iMovie.
If you cannot do that, save the individual clips and components of the original, and export the finished movie in QuickTime format, as those should remain usable in the current release, but you will then need to rebuild the original project. This might seem nugatory effort, but given the many improvements in iMovie over the years, the end result should be worth it.
Updated from the original, which was first published in MacUser volume 27 issue 5, 2011.