When importing media using iMovie 5 or earlier, large video and audio files will be split into multiple clips in the Shelf. Each clip of DV video has a maximum length of about 9 minutes.
iMovie saves imported video in large, full-quality DV format. Because DV clips contain a lot of data, they can be very large files.
Earlier versions of Mac OS had a file size limitation of 2 gigabytes (GB). For compatibility with earlier versions of Mac OS, iMovie does not create files larger than 2 GB when it imports media. If you exceed this limit by capturing a clip that is very long, iMovie splits the clip, and continues capturing into another clip, and continues doing this until the capture is completed. The maximum length of an individual DV movie clip in this case is limited to approximately 9 minutes. The length of other media will vary depending on the type of data.
To play back multiple clips as a single sequence when editing your movie, drag the clips to the Timeline in the correct order.