Ogg Vorbis. In my case the plug-in seemed to cache a lot more data than only the Vorbis Comments, resulting in Windows Media Player 11 eating up the whole swap file, which is statically set to 1.5 GB (twice the 768 MB of RAM available on this computer). After a while adding the entire collection of 253 albums to the Media Library at once caused Windows XP to send a notification that the swap file had been too small and therefore its size had been increased. Note that this only happened during the process of adding Vorbis encodings to the Media Library, not while reading the tags of files (via "Refresh Now!") that had already been added to it before.
The memory leak could easily be tracked in Windows' task manager during scanning, wmplayer.exe was reported to be using a lot more more than 200.000 K of RAM (don't remember the exact figures anymore) when I finally killed the process due to stability issues caused by it. The swap file extended by Windows XP was filled with around 1.8 GB of temporary data in this moment. At least the files which had been added weren't lost because of this measure, allowing me to complete the scan in a second attempt.
Besides, I remember having had exactly the same problems with FLAC using the 1.2 version of your plug-in, though data not handled by it, like the few MP3s and WMAs found on my machine, never caused any issues when being added to the Media Library.
The problem might be related to certain hardware/software configurations, hence my system's specs:
Intel Pentium IV @2.6 Ghz
768 MB of RAM, 1.5 GB swap file
ATI Radeon 9700 XT (special Dell brand) with Omegadrivers 3.8.330
Creative Soundblaster Audigy 2, 5.12.4.1196 drivers
Windows XP Professional with Service Pack 2, including all available security updates
Windows Media Player 11
The system usually is a very clean and stable one, since it's regularly scanned for viruses, adware and spyware as well as erronous and invalid entries in the registry. Processes running in the background, which could interfere with wmplayer.exe, are kept at a minimum. Nonetheless, here's a list of the ones loaded at system startup:
Logfile of HijackThis v1.99.1
Scan saved at 20:47:37, on 27.02.2007
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v7.00 (7.00.6000.16414)
Running processes:
D:\WINXP\System32\smss.exe
D:\WINXP\system32\winlogon.exe
D:\WINXP\system32\services.exe
D:\WINXP\system32\lsass.exe
D:\WINXP\system32\Ati2evxx.exe
D:\WINXP\system32\svchost.exe
D:\WINXP\System32\svchost.exe
D:\WINXP\system32\Ati2evxx.exe
D:\WINXP\system32\ZONELABS\vsmon.exe
D:\WINXP\system32\spoolsv.exe
D:\PROGRA~1\Grisoft\AVG7\avgamsvr.exe
D:\PROGRA~1\Grisoft\AVG7\avgupsvc.exe
D:\PROGRA~1\Grisoft\AVG7\avgemc.exe
D:\WINXP\System32\rsvp.exe
D:\WINXP\System32\snmp.exe
D:\WINXP\System32\svchost.exe
D:\WINXP\Explorer.EXE
D:\Programme\Zone Labs\ZoneAlarm\zlclient.exe
D:\PROGRA~1\Grisoft\AVG7\avgcc.exe
D:\Programme\Microsoft IntelliType Pro\type32.exe
D:\WINXP\system32\wuauclt.exe
D:\Dokumente und Einstellungen\Tobias\Eigene Dateien\HijackThis\HijackThis.exe
O2 - BHO: Adobe PDF Reader - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - D:\Programme\Gemeinsame Dateien\Adobe\Acrobat\ActiveX\AcroIEHelper.dll
O2 - BHO: SSVHelper Class - {761497BB-D6F0-462C-B6EB-D4DAF1D92D43} - D:\Programme\Java\jre1.5.0_08\bin\ssv.dll
O4 - HKLM\..\Run: [ZoneAlarm Client] "D:\Programme\Zone Labs\ZoneAlarm\zlclient.exe"
O4 - HKLM\..\Run: [AVG7_CC] D:\PROGRA~1\Grisoft\AVG7\avgcc.exe /STARTUP
O4 - HKLM\..\Run: [type32] "D:\Programme\Microsoft IntelliType Pro\type32.exe"
O16 - DPF: {5ED80217-570B-4DA9-BF44-BE107C0EC166} (Windows Live Safety Center Base Module) - [url=http://cdn.scan.onecare.live.com/resource/download/scanner/wlscbase9602.cab]http://cdn.scan.onecare.live.com/resource/...lscbase9602.cab[/url]
O16 - DPF: {6414512B-B978-451D-A0D8-FCFDF33E833C} (WUWebControl Class) - [url=http://update.microsoft.com/windowsupdate/v6/V5Controls/en/x86/client/wuweb_site.cab?1158063345593]http://update.microsoft.com/windowsupdate/...b?1158063345593[/url]
O20 - Winlogon Notify: WgaLogon - D:\WINXP\SYSTEM32\WgaLogon.dll
O21 - SSODL: WPDShServiceObj - {AAA288BA-9A4C-45B0-95D7-94D524869DB5} - D:\WINXP\system32\WPDShServiceObj.dll
O23 - Service: Ati HotKey Poller - ATI Technologies Inc. - D:\WINXP\system32\Ati2evxx.exe
O23 - Service: ATI Smart - Unknown owner - D:\WINXP\system32\ati2sgag.exe
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - D:\PROGRA~1\Grisoft\AVG7\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - D:\PROGRA~1\Grisoft\AVG7\avgupsvc.exe
O23 - Service: AVG E-mail Scanner (AVGEMS) - GRISOFT, s.r.o. - D:\PROGRA~1\Grisoft\AVG7\avgemc.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - D:\Programme\Gemeinsame Dateien\InstallShield\Driver\11\Intel 32\IDriverT.exe
O23 - Service: Intel® NMS (NMSSvc) - Intel Corporation - D:\WINXP\System32\NMSSvc.exe
O23 - Service: TrueVector Internet Monitor (vsmon) - Zone Labs, LLC - D:\WINXP\system32\ZONELABS\vsmon.exe