Composing Video and Audio - Video's audio is gone

Question

My question is, I am using the function below, to compose a video and audio. I want to keep video\'s original sound but it goes away somehow, I do not have any clue.

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Answer 1

I figured it out. It seems an AVAsset which loads a video holds the audio and video separately. So you can reach them writing``

videoAsset.tracks(withMediaType: AVMediaTypeAudio)[0] //audio of a video
videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0] //video of a video(without sound)

So I added these lines to the code and it worked!

var mutableCompositionBackTrack : [AVMutableCompositionTrack] = []

mutableCompositionBackTrack.append(mixComposition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: kCMPersistentTrackID_Invalid)) 

try mutableCompositionBackTrack[0].insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAssetTrack.timeRange.duration), of: backAssetTrack, at: kCMTimeZero)

There is a still missing point that I do not know how to do, and that is setting volumes of these audio assets. I will update this answer as soon as I figure out how.