From 1e37a264f10445ed2ccb33d5daf864c3b0d105e9 Mon Sep 17 00:00:00 2001
From: Tom Finegan <tomfinegan@google.com>
Date: Thu, 19 Jan 2012 16:37:11 -0500
Subject: [PATCH] mkvmuxer: Add element start notification.

Just before the first byte of an element identifier is written
the muxer calls IMkvWriter::ElementStartNotify to report the
position of the element in the WebM stream.

Change-Id: Iac40090587bd9496b05f41203aace00902f5606e
---
 mkvmuxer.hpp     | 7 +++++++
 mkvmuxerutil.cpp | 2 ++
 mkvwriter.cpp    | 3 +++
 mkvwriter.hpp    | 1 +
 4 files changed, 13 insertions(+)

diff --git a/mkvmuxer.hpp b/mkvmuxer.hpp
index f42038a..1cb29d8 100644
--- a/mkvmuxer.hpp
+++ b/mkvmuxer.hpp
@@ -35,6 +35,13 @@ class IMkvWriter {
   // Returns true if the writer is seekable.
   virtual bool Seekable() const = 0;
 
+  // Element start notification. Called whenever an element identifier is about
+  // to be written to the stream. |element_id| is the element identifier, and
+  // |position| is the location in the WebM stream where the first octet of the
+  // element identifier will be written.
+  // Note: the |MkvId| enumeration in webmids.hpp defines element values.
+  virtual void ElementStartNotify(uint64 element_id, int64 position) = 0;
+
  protected:
   IMkvWriter();
   virtual ~IMkvWriter();
diff --git a/mkvmuxerutil.cpp b/mkvmuxerutil.cpp
index 3a5739f..2136ff5 100644
--- a/mkvmuxerutil.cpp
+++ b/mkvmuxerutil.cpp
@@ -213,6 +213,8 @@ int32 WriteID(IMkvWriter* writer, uint64 type) {
   if (!writer)
     return -1;
 
+  writer->ElementStartNotify(type, writer->Position());
+
   const int32 size = GetUIntSize(type);
 
   return SerializeInt(writer, type, size);
diff --git a/mkvwriter.cpp b/mkvwriter.cpp
index a71455d..3492141 100644
--- a/mkvwriter.cpp
+++ b/mkvwriter.cpp
@@ -88,4 +88,7 @@ bool MkvWriter::Seekable() const {
   return true;
 }
 
+void MkvWriter::ElementStartNotify(uint64, int64) {
+}
+
 }  // namespace mkvmuxer
diff --git a/mkvwriter.hpp b/mkvwriter.hpp
index 6838f03..8bae247 100644
--- a/mkvwriter.hpp
+++ b/mkvwriter.hpp
@@ -26,6 +26,7 @@ class MkvWriter : public IMkvWriter {
   virtual int64 Position() const;
   virtual int32 Position(int64 position);
   virtual bool Seekable() const;
+  virtual void ElementStartNotify(uint64 element_id, int64 position);
   virtual int32 Write(const void* buffer, uint32 length);
 
   // Creates and opens a file for writing. |filename| is the name of the file