Mp3读取，Effect Remove

Signed-off-by: TRAfoer <lhf190@outlook.com>

Assets/NLayer/Decoder/FrameBase.cs

@@ -0,0 +1,98 @@
+using System;
+
+namespace NLayer.Decoder
+{
+    abstract class FrameBase
+    {
+        static int _totalAllocation = 0;
+        static internal int TotalAllocation
+        {
+            get { return System.Threading.Interlocked.CompareExchange(ref _totalAllocation, 0, 0); }
+        }
+
+        internal long Offset { get; private set; }
+        internal int Length { get; set; }
+
+        MpegStreamReader _reader;
+
+        byte[] _savedBuffer;
+
+        protected FrameBase() { }
+
+        internal bool Validate(long offset, MpegStreamReader reader)
+        {
+            Offset = offset;
+            _reader = reader;
+
+            var len = Validate();
+
+            if (len > 0)
+            {
+                Length = len;
+                return true;
+            }
+            return false;
+        }
+
+        protected int Read(int offset, byte[] buffer)
+        {
+            return Read(offset, buffer, 0, buffer.Length);
+        }
+
+        protected int Read(int offset, byte[] buffer, int index, int count)
+        {
+            if (_savedBuffer != null)
+            {
+                if (index < 0 || index + count > buffer.Length) return 0;   // check against caller's buffer
+                if (offset < 0 || offset >= _savedBuffer.Length) return 0;  // check against saved buffer
+                if (offset + count > _savedBuffer.Length) count = _savedBuffer.Length - index;  // twiddle the size as needed
+
+                Array.Copy(_savedBuffer, offset, buffer, index, count);
+                return count;
+            }
+            else
+            {
+                return _reader.Read(Offset + offset, buffer, index, count);
+            }
+        }
+
+        protected int ReadByte(int offset)
+        {
+            if (_savedBuffer != null)
+            {
+                if (offset < 0) throw new ArgumentOutOfRangeException();
+                if (offset >= _savedBuffer.Length) return -1;
+
+                return (int)_savedBuffer[offset];
+            }
+            else
+            {
+                return _reader.ReadByte(Offset + offset);
+            }
+        }
+
+        /// <summary>
+        /// Called to validate the frame header
+        /// </summary>
+        /// <returns>The length of the frame, or -1 if frame is invalid</returns>
+        abstract protected int Validate();
+
+        internal void SaveBuffer()
+        {
+            _savedBuffer = new byte[Length];
+            _reader.Read(Offset, _savedBuffer, 0, Length);
+            System.Threading.Interlocked.Add(ref _totalAllocation, Length);
+        }
+
+        internal void ClearBuffer()
+        {
+            System.Threading.Interlocked.Add(ref _totalAllocation, -Length);
+            _savedBuffer = null;
+        }
+
+        /// <summary>
+        /// Called when the stream is not "seek-able"
+        /// </summary>
+        virtual internal void Parse() { }
+    }
+}