Make sure the video section and audio section are aligned and start at exactly the same time.
Many variable bitrate or variable frame rate videos cannot be synchronized accurately. When capturing video, be sure to use a constant bitrate and frame rate. In some
cases, you may be able to use the File | Meld Project To Video File
to save the video in a constant bitrate format.
Variable bitrate MP3 files cannot be synchronized at all. Do not use variable bitrate MP3 files. Convert them to a fixed bitrate or Wave format instead. Use
File | Meld Project To Audio File on a project containing only the problem file,
then use the melded file instead.
Start playing the project from time 00:00. When you start playback within the middle of a video or audio section, the synchronization will be off for variable bitrate files.
Increase the frame rate setting under Options | Playback Settings to match the video so that interframe seeking is not required during preview playback.
Use Options | Section Settings and adjust the speed of either the audio section or the video section to compensate for different playback speeds.