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Video lagging behind Audio

When there is a lag between the Audio and the Video, it can be because there are a lot of video frames and the computer can not display them as fast as the Audio can play the samples. However, this does not affect the rendered media in that the Audio and Video will be correctly synchronized. When playing the original media, you can alleviate the lag between the Audio and Video by disabling Play every frame in Settings → Preferences, Playback A tab. Now frames will be skipped in order to keep the audio/video in synch.