Edit HW Audio Tempo in Audacity to Sync with HW Video
The Audacity App can be used to sync HW audio with video. It is free, open source, cross-platform software for recording and editing sounds.
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To begin, you need to determine the offset between the video and HW wav file. Using iMovie and maximum zoom, you first should align the start by comparing the Video Audio track with the HW audio. Trim the beginning so the audio and video will start after about 1/4 second. You can always add a Title and Introduction later.
Then determine the offset in milliseconds at the end. See Determine Offset for details.
Import the HW wav file into Audacity. The adjacent figure shows a stereo setting. A mono setting will contain only one audio trace. Double-click the trace and note the End of Selection. The example indicates 3 minutes and 10.910 seconds (190.910 seconds).
In Audacity, select Effect>Change Tempo. This allows the adjustment of the overall audio length without changing the pitch of each note. Change Speed will adjust the overall length, but will change the pitch, which is not desired.
The Change Tempo window will popup. In the example shown, I am slowing the overall time by 0.3 seconds (190.91 to 190.61). This is 9 frames at 30 fps.
To speed up by .3 (if the audio ends before the video), enter 191.21.
Click OK.
Note the new End Time is the desired 3 minutes and 10.610 seconds.
Now save and import back into iMovie, realign, and finish creating the synchronized movie.
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