问在AudioLayout中检测AVAssetTrack

EN

  if let formatDescriptions = track.formatDescriptions as? [CMAudioFormatDescription],
        let audioFormatDesc = formatDescriptions.first,
        let asbd = CMAudioFormatDescriptionGetStreamBasicDescription(audioFormatDesc)
    {                                   
       //First way to detect number of channels
        numChannels = asbd.pointee.mChannelsPerFrame 
        
        var aclSize:size_t = 0
        var currentChannelLayout:UnsafePointer<AudioChannelLayout>? = nil
            
        currentChannelLayout = CMAudioFormatDescriptionGetChannelLayout(audioFormatDesc, sizeOut: &aclSize)
        
        if let currentChannelLayout = currentChannelLayout, aclSize > 0 {
            let channelLayout = currentChannelLayout.pointee
            
            //second way of detecting number of channels
            numChannels = AudioChannelLayoutTag_GetNumberOfChannels(channelLayout.mChannelLayoutTag) 
        }

}