1 Reply
      Latest reply on Jul 1, 2019 3:40 AM by stef.b
      nuthinking Level 1 Level 1 (0 points)

        I am using AVAudioEngine to analyse some audio tracks and quite often the `while engine.manualRenderingSampleTime < sourceFile.length {` loop takes a moment to start receiving audio data. Looking at the soundwave looks like the input is simply delayed. This wouldn't be a problem if the length of the buffer would vary depending on this latency but the length unfortunately stays always the same, loosing the final part of the track.

        I took the code from the official tutorial and this seems to happen regardless if I add an EQ effect or not. Actually looks like the two analysis (with or without EQ) done one after the other return the same anomaly.



            let format: AVAudioFormat = sourceFile.processingFormat
            let engine = AVAudioEngine()
            let player = AVAudioPlayerNode()
            if compress {
                let eq = AVAudioUnitEQ(numberOfBands: 2)
                let lowPass = eq.bands[0]
                lowPass.filterType = .lowPass
                lowPass.frequency = 150.0
                lowPass.bypass = false
                let highPass = eq.bands[1]
                highPass.filterType = .highPass
                highPass.frequency = 100.0
                highPass.bypass = false
                engine.connect(player, to: eq, format: format)
                engine.connect(eq, to: engine.mainMixerNode, format: format)
                engine.connect(player, to: engine.mainMixerNode, format: format)
            do {
                let maxNumberOfFrames: AVAudioFrameCount = 4096
                try engine.enableManualRenderingMode(.offline, format: format, maximumFrameCount: maxNumberOfFrames)
            } catch {
                fatalError("Could not enable manual rendering mode, \(error)")
            player.scheduleFile(sourceFile, at: nil)
            do {
                try engine.start()
                fatalError("Could not start engine, \(error)")
            // buffer to which the engine will render the processed data
            let buffer: AVAudioPCMBuffer = AVAudioPCMBuffer(pcmFormat: engine.manualRenderingFormat, frameCapacity: engine.manualRenderingMaximumFrameCount)!
            var pi = 0
            while engine.manualRenderingSampleTime < sourceFile.length {
                do {
                    let framesToRender = min(buffer.frameCapacity, AVAudioFrameCount(sourceFile.length - engine.manualRenderingSampleTime))
                    let status = try engine.renderOffline(framesToRender, to: buffer)
                    switch status {
                    case .success:
                        // data rendered successfully
                        let flength = Int(buffer.frameLength)
                        points.reserveCapacity(pi + flength)
                        if let chans = buffer.floatChannelData?.pointee {
                            let left = chans.advanced(by: 0)
                            let right = chans.advanced(by: 1)
                            for b in 0..<flength {
                                let v:Float = max(abs(left[b]), abs(right[b]))
                        pi += flength
                    case .insufficientDataFromInputNode:
                        // applicable only if using the input node as one of the sources
                    case .cannotDoInCurrentContext:
                        // engine could not render in the current render call, retry in next iteration
                    case .error:
                        // error occurred while rendering
                        fatalError("render failed")
                } catch {
                    fatalError("render failed, \(error)")


        I thought it was perhaps a simulator issue, but also on the device is happening. Am I doing anything wrong? Thanks!