swift: how to delete part of audio?

Question

I\'m creating a simple audio editing tool to trim and delete from an audio. I implemented the trim function and it is working fine. However I searched and tried to implement

Answer 1

CMTimeRangeGetUnion returns another CMTimeRange, which is just a (start-)time and a duration. So there is nothing than can hold the two time ranges required to do what you are expecting. In extension, AVAssetExportSession has no API that takes a list of time ranges to export.

But there is a way to accomplish it. The idea is to create an editable copy of the asset, delete the time range, and then export the editable copy. AVMutableComposition does this:

// assuming 'asset', 'endTimeOfRange1' and 'startTimeOfRange2' from the question:

// create empty mutable composition
let composition: AVMutableComposition = AVMutableComposition()
// copy all of original asset into the mutable composition, effectively creating an editable copy
try composition.insertTimeRange( CMTimeRangeMake( kCMTimeZero, asset.duration), of: asset, at: kCMTimeZero)

// now edit as required, e.g. delete a time range
let startTime = CMTime(seconds: endTimeOfRange1, preferredTimescale: 100)
let endTime = CMTime(seconds: startTimeOfRange2, preferredTimescale: 100)
composition.removeTimeRange( CMTimeRangeFromTimeToTime( startTime, endTime))

// since AVMutableComposition is an AVAsset subclass, it can be exported with AVAssetExportSession (or played with an AVPlayer(Item))
if let exporter = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A) 
{
    // configure session and exportAsynchronously as above. 
    // You don't have to set the timeRange of the exportSession
}

Note that copying from the asset to the composition only modifies some in-memory structures defining which samples go where on the time line, but doesn't actually moves any media samples around. This is not done until exporting; as result, editing is (relatively) fast, and you have to keep the source file around at least until export is finished.