FLV: Detect duplicated data by using hashes

TODO: fix test data

BililiveRecorder.Flv/Pipeline/Rules/RemoveDuplicatedChunkRule.cs

@@ -1,8 +1,13 @@
 using System;
+using System.Buffers;
+using System.Buffers.Binary;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
+using System.Text;
 using BililiveRecorder.Flv;
 using BililiveRecorder.Flv.Pipeline.Actions;
+using FastHashes;
 using StructLinq;
 
 namespace BililiveRecorder.Flv.Pipeline.Rules
@@ -12,10 +17,11 @@ namespace BililiveRecorder.Flv.Pipeline.Rules
     /// </summary>
     public class RemoveDuplicatedChunkRule : ISimpleProcessingRule
     {
-        private const int MAX_HISTORY = 8;
+        private const int MAX_HISTORY = 16;
         private const string QUEUE_KEY = "DeDuplicationQueue";
 
-        private static readonly ProcessingComment comment = new ProcessingComment(CommentType.RepeatingData, "发现了重复的 Flv Chunk");
+        private static readonly FarmHash64 farmHash64 = new();
+        private static readonly ProcessingComment comment = new ProcessingComment(CommentType.RepeatingData, "重复数据");
 
         public void Run(FlvProcessingContext context, Action next)
         {
@@ -27,67 +33,56 @@ namespace BililiveRecorder.Flv.Pipeline.Rules
         {
             if (action is PipelineDataAction data)
             {
-                var feature = new List<long>(data.Tags.Count * 2 + 1)
-                {
-                    data.Tags.Count
-                };
+                var tagHashs = new MemoryStream(4 + data.Tags.Count * 16);
 
-                unchecked
                 {
-                    // TODO: 改成用 Hash 判断
-                    // 计算一个特征码
-                    // 此处并没有遵循什么特定的算法，只是随便取了一些代表性比较强的值，用简单又尽量可靠的方式糅合到一起而已
+                    var buffer = ArrayPool<byte>.Shared.Rent(4);
+                    try
+                    {
+                        BinaryPrimitives.WriteInt32BigEndian(buffer, data.Tags.Count);
+                        tagHashs.Write(buffer, 0, 4);
+                    }
+                    finally
+                    {
+                        ArrayPool<byte>.Shared.Return(buffer);
+                    }
+                }
+
                 foreach (var tag in data.Tags)
                 {
-                        var f = 0L;
-                        f ^= tag.Type switch
+                    var tagHash = tag.DataHash ?? tag.UpdateDataHash();
+                    if (tagHash is not null)
                     {
-                            TagType.Audio => 0b01,
-                            TagType.Video => 0b10,
-                            TagType.Script => 0b11,
-                            _ => 0b00,
-                        };
-                        f <<= 3;
-                        f ^= (int)tag.Flag & ((1 << 3) - 1);
-                        f <<= 32;
-                        f ^= tag.Timestamp;
-                        f <<= 32 - 5;
-                        f ^= tag.Size & ((1 << (32 - 5)) - 1);
-                        feature.Add(f);
+                        var bytes = Encoding.UTF8.GetBytes(tagHash);
+                        tagHashs.Write(bytes, 0, bytes.Length);
+                    }
+                }
 
-                        if (tag.Nalus == null)
-                            feature.Add(long.MinValue);
-                        else
-                        {
-                            long n = tag.Nalus.Count << 32;
-                            foreach (var nalu in tag.Nalus)
-                                n ^= (((int)nalu.Type) << 16) ^ ((int)nalu.FullSize);
-                            feature.Add(n);
-                        }
-                    }
-                }
+                var hash = farmHash64.ComputeHash(tagHashs.GetBuffer(), (int)tagHashs.Length);
 
                 // 存储最近 MAX_HISTORY 个 Data Chunk 的特征的 Queue
-                Queue<List<long>> history;
-                if (context.SessionItems.TryGetValue(QUEUE_KEY, out var obj) && obj is Queue<List<long>> q)
-                    history = q;
+                Queue<byte[]> hashHistory;
+                if (context.SessionItems.TryGetValue(QUEUE_KEY, out var obj) && obj is Queue<byte[]> q)
+                    hashHistory = q;
                 else
                 {
-                    history = new Queue<List<long>>(MAX_HISTORY + 1);
-                    context.SessionItems[QUEUE_KEY] = history;
+                    hashHistory = new Queue<byte[]>(MAX_HISTORY + 1);
+                    context.SessionItems[QUEUE_KEY] = hashHistory;
                 }
 
                 // 对比历史特征
-                if (history.ToStructEnumerable().Any(x => x.SequenceEqual(feature), x => x))
+                if (hashHistory.ToStructEnumerable().Any(x => x.SequenceEqual(hash), x => x))
                 {
+                    // 重复数据                    
                     context.AddComment(comment);
                 }
                 else
                 {
-                    history.Enqueue(feature);
+                    // 新数据
+                    hashHistory.Enqueue(hash);
 
-                    while (history.Count > MAX_HISTORY)
-                        history.Dequeue();
+                    while (hashHistory.Count > MAX_HISTORY)
+                        hashHistory.Dequeue();
 
                     yield return action;
                 }