Setting multiple Volumes to each Video tracks using AudioMixInputParameters AVFoundation is not working in Swift iOS

Question

I am working on Video based Application in Swift. As per the requirement I have to select multiple Videos from Devi

Answer 1

I found, that exporting an asset with preset of AVAssetExportPresetPassthrough doesn't have an impact on output volume. When I tried to use AVAssetExportPresetLowQuality, volume change successfully applied.

I wish it is better documented somewhere :(

The working code:

// Assume we have:
let composition: AVMutableComposition
var inputParameters = [AVAudioMixInputParameters]()

// We add a track
let trackComposition = composition.addMutableTrack(...)

// Configure volume for this track
let inputParameter = AVMutableAudioMixInputParameters(track: trackComposition)
inputParameter.setVolume(desiredVolume, at: startTime)

// It works even without setting the `trackID`
// inputParameter.trackID = trackComposition.trackID

inputParameters.append(inputParameter)

// Apply gathered `inputParameters` before exporting
let audioMix = AVMutableAudioMix()
audioMix.inputParameters = inputParameters

// I found it's not working, if using `AVAssetExportPresetPassthrough`,
// so try `AVAssetExportPresetLowQuality` first
let export = AVAssetExportSession(..., presetName: AVAssetExportPresetLowQuality)
export.audioMix = audioMix

Tested this with multiple assetTrack insertions to the same compositionTrack, setting different volume for each insertion. Seems to be working.