How to Put Clean Audio Back Into a Video

The short version

Clean the audio on its own first, then put it back.
Replace the audio track and copy the video stream: the picture is not re-encoded.
Check the length: a longer audio track is cut to the picture, a shorter one leaves silence.
Keep the original video in case you need it again.

Why the picture should not be re-encoded

Every time a video is re-encoded it loses a little quality. If you only change the sound, the video stream can be copied as it is. That is faster and keeps the picture identical.

The steps

Clean the audio. The phone cleanup and the Perfect it steps in the cleanup guide apply.
Open the video in Tunedzy and choose the replace-audio option. Pick the cleaned file.
Tunedzy copies the picture and writes the new sound beside it. Play the result and check the start, the end and the joins.

Limits

The replacement works for common phone formats (MP4 and MOV), and the picture is copied, not changed. If the new sound is longer than the picture it is cut; if it is shorter, the rest of the video is silent. A video with no picture stream is refused.

On your phone, Tunedzy Go cleans the sound of a recording or a file you choose. Putting the sound back into a video is a Windows app step for now.