What Are Dropped Frames?
Dropped frames are frames that are unintentionally skipped during playback, either
because the hard disk cannot keep up with the video data rate or because the
computer processor cannot perform all of the applied effects in time. Some real-time
playback modes allow dropped frames, while others require rendering to avoid
dropped frames.
Dropped frames during editing are usually tolerable. However, during output,
dropped frames are almost always unacceptable.