Separate AmplitudeProcessor from TrackSDL3

osu.Framework/Audio/Mixing/SDL3/ISDL3AudioChannel.cs

@@ -11,7 +11,7 @@ internal interface ISDL3AudioChannel : IAudioChannel
         /// <summary>
         /// Returns remaining audio samples.
         /// </summary>
-        /// <param name="data">Audio data needs to be put here. Length of this determines how much data needs to be filled.</param>
+        /// <param name="data">Channel puts audio in this array. Length of this determines how much data needs to be filled.</param>
         /// <returns>Sample count</returns>
         int GetRemainingSamples(float[] data);
 

osu.Framework/Audio/SDL3AmplitudeProcessor.cs

@@ -0,0 +1,52 @@
+// Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using NAudio.Dsp;
+using osu.Framework.Audio.Track;
+using osu.Framework.Extensions;
+
+namespace osu.Framework.Audio
+{
+    internal class SDL3AmplitudeProcessor
+    {
+        /// <summary>
+        /// The most recent amplitude data. Note that this is updated on an ongoing basis and there is no guarantee it is in a consistent (single sample) state.
+        /// If you need consistent data, make a copy of FrequencyAmplitudes while on the audio thread.
+        /// </summary>
+        public ChannelAmplitudes CurrentAmplitudes { get; private set; } = ChannelAmplitudes.Empty;
+
+        private Complex[] fftSamples = new Complex[ChannelAmplitudes.AMPLITUDES_SIZE * 2];
+        private float[] fftResult = new float[ChannelAmplitudes.AMPLITUDES_SIZE];
+
+        public void Update(float[] samples, int channels)
+        {
+            if (samples.Length / channels < ChannelAmplitudes.AMPLITUDES_SIZE)
+                return; // not enough data
+
+            float leftAmplitude = 0;
+            float rightAmplitude = 0;
+            int secondCh = channels < 2 ? 0 : 1;
+            int fftIndex = 0;
+
+            for (int i = 0; i < samples.Length; i += channels)
+            {
+                leftAmplitude = Math.Max(leftAmplitude, Math.Abs(samples[i]));
+                rightAmplitude = Math.Max(rightAmplitude, Math.Abs(samples[i + secondCh]));
+
+                if (fftIndex < fftSamples.Length)
+                {
+                    fftSamples[fftIndex].Y = 0;
+                    fftSamples[fftIndex++].X = samples[i] + samples[i + secondCh];
+                }
+            }
+
+            FastFourierTransform.FFT(true, (int)Math.Log2(fftSamples.Length), fftSamples);
+
+            for (int i = 0; i < fftResult.Length; i++)
+                fftResult[i] = fftSamples[i].ComputeMagnitude();
+
+            CurrentAmplitudes = new ChannelAmplitudes(Math.Min(1f, leftAmplitude), Math.Min(1f, rightAmplitude), fftResult);
+        }
+    }
+}

osu.Framework/Audio/Track/TrackSDL3.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Threading;
 using System.Threading.Tasks;
-using NAudio.Dsp;
 using osu.Framework.Audio.Mixing.SDL3;
 using osu.Framework.Extensions;
 using osu.Framework.Logging;
@@ -100,57 +99,12 @@ void ISDL3AudioDataReceiver.GetMetaData(int bitrate, double length, long byteLen
             }
         }
 
-        private volatile bool amplitudeRequested;
         private double lastTime;
-
-        private ChannelAmplitudes currentAmplitudes = ChannelAmplitudes.Empty;
         private float[]? samples;
-        private Complex[]? fftSamples;
-        private float[]? fftResult;
-
-        public override ChannelAmplitudes CurrentAmplitudes
-        {
-            get
-            {
-                if (!amplitudeRequested)
-                    amplitudeRequested = true;
-
-                return isRunning ? currentAmplitudes : ChannelAmplitudes.Empty;
-            }
-        }
-
-        private void updateCurrentAmplitude()
-        {
-            samples ??= new float[(int)(player.SrcRate * (1f / 60)) * player.SrcChannels];
-            fftSamples ??= new Complex[ChannelAmplitudes.AMPLITUDES_SIZE * 2];
-            fftResult ??= new float[ChannelAmplitudes.AMPLITUDES_SIZE];
-
-            player.Peek(samples, lastTime);
 
-            float leftAmplitude = 0;
-            float rightAmplitude = 0;
-            int secondCh = player.SrcChannels < 2 ? 0 : 1;
-            int fftIndex = 0;
+        private SDL3AmplitudeProcessor? amplitudeProcessor;
 
-            for (int i = 0; i < samples.Length; i += player.SrcChannels)
-            {
-                leftAmplitude = Math.Max(leftAmplitude, Math.Abs(samples[i]));
-                rightAmplitude = Math.Max(rightAmplitude, Math.Abs(samples[i + secondCh]));
-
-                if (fftIndex < fftSamples.Length)
-                {
-                    fftSamples[fftIndex].Y = 0;
-                    fftSamples[fftIndex++].X = samples[i] + samples[i + secondCh];
-                }
-            }
-
-            FastFourierTransform.FFT(true, (int)Math.Log2(fftSamples.Length), fftSamples);
-
-            for (int i = 0; i < fftResult.Length; i++)
-                fftResult[i] = fftSamples[i].ComputeMagnitude();
-
-            currentAmplitudes = new ChannelAmplitudes(Math.Min(1f, leftAmplitude), Math.Min(1f, rightAmplitude), fftResult);
-        }
+        public override ChannelAmplitudes CurrentAmplitudes => (amplitudeProcessor ??= new SDL3AmplitudeProcessor()).CurrentAmplitudes;
 
         protected override void UpdateState()
         {
@@ -176,12 +130,13 @@ protected override void UpdateState()
                     player.FillRequiredSamples();
             }
 
-            // Not sure if I need to split this up to another class since this feature is only exclusive to Track
-            if (amplitudeRequested && isRunning && Math.Abs(currentTime - lastTime) > 1000.0 / 60.0)
+            if (amplitudeProcessor != null && isRunning && Math.Abs(currentTime - lastTime) > 1000.0 / 60.0)
             {
                 lastTime = currentTime;
+                samples ??= new float[(int)(player.SrcRate * (1f / 60)) * player.SrcChannels];
+                player.Peek(samples, lastTime);
 
-                updateCurrentAmplitude();
+                amplitudeProcessor.Update(samples, player.SrcChannels);
             }
         }