Add Audio Avisynth

AddAudio - Avisynth wiki

http://avisynth.nl/index.php/AddAudio#:~:text=Therefore%20a%20function%20has%20been%20made%20to%20add,%28audio_rate%3D44100%2Csixteen_bit%3Dtrue%2Cstereo%3Dtrue%2Clength%3Dv1.FrameCount%2Cfps%3Dv1.FrameRate%29%20v1%20%3D%20AudioDub%20%28v1%2Cv2%29%20return%20v1%20%7D

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AddAudio - Avisynth wiki

http://avisynth.nl/index.php/AddAudio

AVIsynth -- how do I add an audio wav to a video only clip ...

https://forum.videohelp.com/threads/293908-AVIsynth-how-do-I-add-an-audio-wav-to-a-video-only-clip-%5bSOLVED%5d

I need to feed a video only source and then mux in the .wav audio because I am manipulaint the framerate and if I add (mux) the audio in later, it will mess things up a bit. I want to avoid it and just feed the vid/aud in the first avisynth script before doing any framerate conversion stuff.

Importing media - Avisynth wiki

http://avisynth.nl/index.php/Importing_media

AudioDub - Avisynth wiki

http://avisynth.nl/index.php/AudioDub

Add Some Volume to Audio Tracks Via Avisynth Script ...

http://www.digitalfaq.com/archives/avisynth/14592-add-volume-audio.html

I don't know about audio managemetn in avisynth as it is mostly a frame server (dedicated to image so). But your question suggest that you are encoding audio directly with the tool that encodes also the video.