From 8e6310a62886d82ee728be4a3348fce9ab0f90ef Mon Sep 17 00:00:00 2001
From: AlekseyMartynov <AlekseyMartynov@users.noreply.github.com>
Date: Mon, 11 Sep 2023 12:04:00 +0300
Subject: [PATCH] `sampleCount` difference puzzle (9dd7b3680) solved

---
 Tagging/Sig.cs                   |  5 +----
 Test/SignatureComparisonTests.cs | 21 +++++++++++++--------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/Tagging/Sig.cs b/Tagging/Sig.cs
index 6ae90e1..a047fcc 100644
--- a/Tagging/Sig.cs
+++ b/Tagging/Sig.cs
@@ -10,9 +10,6 @@ namespace Project;
 static class Sig {
 
     public static byte[] Write(int sampleRate, int sampleCount, PeakFinder finder) {
-        // https://github.com/marin-m/SongRec/blob/0.3.2/src/fingerprinting/signature_format.rs#L238
-        var sampleCountPadding = sampleRate * 6 / 25;
-
         using(var mem = new MemoryStream())
         using(var writer = new BinaryWriter(mem)) {
             writer.Write(0xCAFE2580); // Dialling "2580" on your phone and holding it up to the music, https://www.shazam.com/company
@@ -25,7 +22,7 @@ public static byte[] Write(int sampleRate, int sampleCount, PeakFinder finder) {
             writer.Write(GetSampleRateCode(sampleRate) << 27);
             writer.Write(0);
             writer.Write(0);
-            writer.Write(sampleCount + sampleCountPadding);
+            writer.Write(sampleCount);
             writer.Write(0x007C0000);
             writer.Write(0x40000000);
             writer.Write(-1);
diff --git a/Test/SignatureComparisonTests.cs b/Test/SignatureComparisonTests.cs
index 6abb1db..f6e7c4d 100644
--- a/Test/SignatureComparisonTests.cs
+++ b/Test/SignatureComparisonTests.cs
@@ -16,6 +16,7 @@ public void Ref_SigX_10_1_3() {
             CreateFromWaveFile(
                 Path.Combine(TestHelper.DATA_DIR, "test2.wav"),
                 out var mySampleCount,
+                out var myRemainingSampleCount,
                 out var myPeaks
             );
 
@@ -26,12 +27,17 @@ out var myPeaks
                 out var refPeaks
             );
 
-            Assert.Equal(refSampleCount, mySampleCount);
+            // Official signature has more peaks
+            // Most of them are at edges < RADIUS_TIME
 
-            var anchorBin = 38;
-            var myStripe = myPeaks.FindOne(anchorBin).StripeIndex;
-            var refStripe = refPeaks.FindOne(anchorBin).StripeIndex;
-            var refStripeOffset = refStripe - myStripe;
+            // Possible explanation for padding in official signature
+            // start - first chunk completes the FFT window so it is immediately ready for analysis
+            // end - to absorb remaining samples? for symmetry?
+
+            var refSampleCountPadding = Analysis.WINDOW_SIZE - Analysis.CHUNK_SIZE;
+            var refStripeOffset = refSampleCountPadding / Analysis.CHUNK_SIZE;
+
+            Assert.Equal(refSampleCount - 2 * refSampleCountPadding, mySampleCount + myRemainingSampleCount);
 
             var hitCount = 0;
             var missCount = 0;
@@ -61,7 +67,7 @@ out var refPeaks
             Assert.True(Math.Abs(magnFitIntercept) < 10);
         }
 
-        static void CreateFromWaveFile(string path, out int sampleCount, out IReadOnlyList<PeakInfo> peaks) {
+        static void CreateFromWaveFile(string path, out int sampleCount, out int remainingSampleCount, out IReadOnlyList<PeakInfo> peaks) {
             var analysis = new Analysis();
             var finder = new PeakFinder(analysis);
 
@@ -69,7 +75,6 @@ static void CreateFromWaveFile(string path, out int sampleCount, out IReadOnlyLi
             var sampleProvider = wave.ToSampleProvider();
 
             var chunk = new float[Analysis.CHUNK_SIZE];
-            var remainingSampleCount = 0;
 
             while(true) {
                 var readCount = sampleProvider.Read(chunk, 0, chunk.Length);
@@ -82,7 +87,7 @@ static void CreateFromWaveFile(string path, out int sampleCount, out IReadOnlyLi
                 analysis.AddChunk(chunk);
             }
 
-            var sigBytes = Sig.Write(Analysis.SAMPLE_RATE, analysis.ProcessedSamples + remainingSampleCount, finder);
+            var sigBytes = Sig.Write(Analysis.SAMPLE_RATE, analysis.ProcessedSamples, finder);
             LoadBinary(sigBytes, out sampleCount, out peaks);
         }