From 989ca7f7934556bd48e44259076932c813410aa8 Mon Sep 17 00:00:00 2001
From: Grigory Chudov <gchudov@gmail.com>
Date: Tue, 3 Jul 2018 19:56:08 -0400
Subject: [PATCH] Implement padding support for mp3 files

---
 CUETools.Codecs.libmp3lame/LameWriter.cs | 30 ++++++++++++++----------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/CUETools.Codecs.libmp3lame/LameWriter.cs b/CUETools.Codecs.libmp3lame/LameWriter.cs
index 8d75af3..661c097 100644
--- a/CUETools.Codecs.libmp3lame/LameWriter.cs
+++ b/CUETools.Codecs.libmp3lame/LameWriter.cs
@@ -15,6 +15,7 @@ namespace CUETools.Codecs.libmp3lame
         private uint m_finalSampleCount;
         private byte[] m_outputBuffer;
         private long m_bytesWritten;
+        private long m_streamStart;
 
         public long FinalSampleCount
         {
@@ -85,7 +86,7 @@ namespace CUETools.Codecs.libmp3lame
             }
 
             int lametagFrameSize = this.GetLametagFrame();
-            this.m_outputStream.Seek(0, SeekOrigin.Begin);
+            this.m_outputStream.Seek(m_streamStart, SeekOrigin.Begin);
             this.m_outputStream.Write(this.m_outputBuffer, 0, lametagFrameSize);
         }
 
@@ -122,6 +123,7 @@ namespace CUETools.Codecs.libmp3lame
 
         private int GetLametagFrame()
         {
+            this.EnsureOutputBufferSize(1024);
             while (true)
             {
                 uint lametagFrameResult;
@@ -144,17 +146,6 @@ namespace CUETools.Codecs.libmp3lame
             }
         }
 
-        public uint GetLametagFrame(byte[] outputBuffer)
-        {
-            unsafe
-            {
-                fixed (byte* outputBufferPtr = outputBuffer)
-                {
-                    return libmp3lamedll.lame_get_lametag_frame(m_handle, (IntPtr)outputBufferPtr, (uint)outputBuffer.Length);
-                }
-            }
-        }
-
         private void EnsureInitialized()
         {
             if (!this.m_initialized)
@@ -179,6 +170,21 @@ namespace CUETools.Codecs.libmp3lame
                     throw new LameException("lame_init_params failed");
                 }
 
+                byte[] id3v2 = { 0x49, 0x44, 0x33, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
+                int padding = m_settings.Padding;
+                int id3v2sz = padding;
+                int i = 9;
+                do
+                {
+                    id3v2[i--] = (byte)(id3v2sz & 0x7f);
+                    id3v2sz >>= 7;
+                } while (id3v2sz != 0);
+                m_outputStream.Write(id3v2, 0, id3v2.Length);
+                m_bytesWritten += id3v2.Length;
+                m_outputStream.Write(new byte[padding], 0, padding);
+                m_bytesWritten += padding;
+                m_streamStart = this.m_outputStream.Position;
+
                 this.m_initialized = true;
             }
         }