音楽ファイルの属性の長さを取得：IWMHeaderInfo::GetAttributeByName

#include <stdio.h>  //printf　とかで必要
#include <wmsdk.h>  //HRESULT　とかで必要

using namespace System;//Console::ReadLine()で必要

#pragma comment(lib, "wmvcore.lib")   //IWMMetadataEditor　とかで必要

void main(){

 HRESULT hr          = S_OK;

 IWMMetadataEditor * pEditor = NULL;
 IWMHeaderInfo3 * pHeaderInfo = NULL;

 WORD stream = 0;
 WMT_ATTR_DATATYPE enumType;
 QWORD duration;
 WORD cbLength = sizeof( duration );

 hr = WMCreateEditor(&pEditor);
 hr = pEditor->Open(L"G:\\sampleMovie\\Amanda.wma");
 hr = pEditor->QueryInterface(IID_IWMHeaderInfo, (void**) &pHeaderInfo);

 hr = pHeaderInfo->GetAttributeByName( &stream, 
  g_wszWMDuration, &enumType,(BYTE *)&duration, &cbLength );

 printf("%d ミリ秒\r\n", (long) (duration / 10000) );

 Console::ReadLine();//入力待-ウインドウ維持

}

4分6秒は246秒