Preparing the Audio for Encoding - A Practical Guide to Video and Audio Compression - page 599

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Preparing the Audio for Encoding

37.1 Audio Preprocessing

Now that the video is preprocessed and ready for encoding, the audio must be processed.
There are several things that need to be checked, although there is no set order to doing
these. Obviously, you want to make sure that each step removes unwanted artifacts with-
out undoing what you did in the previous step.

37.2 Trimming and Cropping

The audio usually accompanies some video, so their durations must be cropped to the
same length. The editing software should be maintaining the edits on the audio track as
the video is cut; otherwise the lip sync is broken. There are occasions when the video and
audio digitizing processes are carried out independently. In those cases, the audio must be
laid alongside the video and carefully trimmed to fit after it has been aligned.

37.3 Synchronizing

Any independently digitized audio must be synchronized; an offset of even a couple of
frames is enough for lip sync to be lost, and that makes for a very unsatisfactory viewing
experience. Check at the start, at the end, and at intervals throughout the movie. Ideally,
you should play it all the way through to check. Depending on how you are doing this,

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