Windows Virtual PC files and locations

Microsoft Windows Virtual PC implements virtual machines and the application holds the entire machine state and virtual hard disk information in files. In a few large files in fact, so a question to move and/or backup the files is a question of periodic interest.

So what are the files it is using? First of all, the primary file a user clicks on to start virtual machine is a .VMCX file and it is located in “C:\Users\$(UserName)\Virtual Machines” directory. It is a shortcut to internal files and is holding very basic information about the machine, its state and location of other files.

<?xml version="1.0" encoding="UTF-16"?>
<!-- Microsoft Virtual Machine Description and Registration Settings -->
    <ram_size type="string">512 MB</ram_size>
    <vmstate type="string">Hibernated</vmstate>
    <primary_disk1 type="string">C:\Users\Roman\AppData\Local\Microsoft\Windows Virtual PC\Virtual Machines\Windows XP Mode.vhd</primary_disk1>
    <secondary_disk1 type="string" />
    <notes type="string">Windows XP Professional in "XP Mode"
Username XPMUser, Password XPM User</notes>
    <vmc_path type="string">C:\Users\Roman\AppData\Local\Microsoft\Windows Virtual PC\Virtual Machines\Windows XP Mode.vmc</vmc_path>

This directory has a special hidden desktop.ini file in it, which instruct the shell to treat the directory and the files in a special way, as Virtual PC files. This is also how Windows is providing user a link “Create virtual machine”.

The .VMCX file is editable (its format is based on XML) and it holds references to .VHD virtual disk files and .VMC virtual machine configuration files. However, .VMCX file is nothing but a shortcut only, and Windows Virtual PC will re-created those files once underlying .VMC file is double-clicked to be started, so there is no need to edit .VMCX files.

.VMC file is a virtual machine configuration file and it holds the settings a user provides for the virtual machine through settings dialog. The file is also using XML formatting, and is editable. While the file is small itself, its location is used as a base location for .VSV file, where software stores runtime state of virtual machine. The .VSV file size is stipulated by amount of RAM granted to the virtual machine, so the file may be pretty large itself and it might be desired to be moved to another location also. To achieve this, the small .VMC file needs to be moved to location of interest. A .VMC file can be double-clicked itself to start the virtual machine.

Windows Virtual PC Settings Dialog

.VHD are the large files as they store data from virtual hard disks, so moving them may make sense. Additionally to the files themselves, if “Create Undo Disks” option is enabled, software will manage additional .VUD file with the name of format “VirtualPCUndo_$(VirtualMachineName)_$(Token).vud” file with changes that has not yet been applied. If moved, the .VUD files have to be thought of as a part of .VHD files.

By default a .VMC file holds both absolute and relative path refrences to .VHD and .VUD files, with relative reference as a priority. So if .VMC and .VHD (optionally with .VUD) files are moved together, no special path update/edit required. Software will be able to locate moved disk file automatically as soon as virtual machine is started. Still it is possible to edit the files manually and have files located in different directories. Also if disk file location is modified via GUI, software offers/attempts to strip undo disk .VUD file and cancel unapplied changes. If configuration file is edited manually, it is possible to keep undo disks without canceling the changes.

When moving files to a different location, make sure to check directory security so that Windows Virtual PC has sufficient privileges accessing files in the new location, or otherwise it would show ambiguous error messages “Could not register the virtual machine”.

See Also: Windows Virtual PC Tips on

MediaTools: How to manually configure filters to render M-JPEG video stream from an IP camera

Media Tools DirectShow Filters can be used to acquire, parse and decoder M-JPEG encoded video stream from an IP camera or a video server, however for a quick start it is necessary to properly register filters on system and create a DirectShow graph.

To register the filters, it is necessary to download DLLs from repository. While Acquisition.dll does not require special prerequisites installed, CodingI.dll is using Intel Integrated Performance Primitives (IPP) version 6.0.0 internally and requires its [at least] redistributables installed before DLLs are being registered using regsvr32.

Intel went further with new releases of IPP, which are incompatible with the version used to build CodingI.dll, so it is version 6.0.0 (in downloads on Intel website: version 6.0 build 0) has to be installed. Note that Intel DLLs from C:\Program Files\Intel\IPP\\ia32\bin (version is known to be also compatible) need to be on system search path, or copied to C:\Windows\system32 directory.

Once Intel IPP is prepared, it is required to register CodingI.dll using regsvr32. This registers filters and they are available in GraphEdit and for applications. It is important that on the way of constructing graph which renders video using standard video renderers it is required to specify correct resolution for video, or otherwise graph might fail to start with a message “The graph could not change state”, caused by video renderer failure to dynamically change to different (effective) resolution.

To create rendering graph, add Alax.Info HTTP Stream Source Filter from the filter list and provide camera URL in properties, e.g.

Adding Alax.Info HTTP Stream Source Filter


How To: Save image to BMP file from IBasicVideo or VMR windowless interface

A simple question being asked all over again. Given IBasicVideo, IBasicVideo2, IVMRWindowlessControl or IVMRWindowlessControl9, how to save image to file? It is easy. It is a bit easier with IBasicVideo because it is possible to query this interface directly from graph’s interface, such as IGraphBuilder, and the call will be forwarded to video renderer. This code assumes internal bitmap format is non-paletted, which I believe is always the case.

LONG nBufferSize = 0;
ATLENSURE_SUCCEEDED(pBasicVideo->GetCurrentImage(&nBufferSize, NULL));
CHeapPtr<BITMAPINFO> pBitmapInfo;
ATLENSURE_THROW(pBitmapInfo.AllocateBytes(nBufferSize), E_OUTOFMEMORY);
ATLENSURE_SUCCEEDED(pBasicVideo->GetCurrentImage(&nBufferSize, (LONG*) (BITMAPINFO*) pBitmapInfo));
const BYTE* pnData = (const BYTE*) (&pBitmapInfo->bmiHeader + 1);
// NOTE: You might wish to handle <=8 bpp bitmaps here
ATLASSERT(pBitmapInfo->bmiHeader.biBitCount > 8);
ATLASSERT(pBitmapInfo->bmiHeader.biCompression == BI_RGB);
ZeroMemory(&BitmapFileHeader, sizeof BitmapFileHeader);
BitmapFileHeader.bfType = 'MB';
BitmapFileHeader.bfSize = (DWORD) (sizeof (BITMAPFILEHEADER) + pBitmapInfo->bmiHeader.biSize + pBitmapInfo->bmiHeader.biSizeImage);
BitmapFileHeader.bfOffBits = (DWORD) (sizeof (BITMAPFILEHEADER) + pBitmapInfo->bmiHeader.biSize);
ATLENSURE_SUCCEEDED(File.Write(&BitmapFileHeader, sizeof BitmapFileHeader));
ATLENSURE_SUCCEEDED(File.Write(&pBitmapInfo->bmiHeader, pBitmapInfo->bmiHeader.biSize));
ATLENSURE_SUCCEEDED(File.Write(pnData, (DWORD) pBitmapInfo->bmiHeader.biSizeImage));

How To: Dump CAtlRegExp regular expression variable on parse error

ATL regular expression code adds dump/debug capabilities with ATL_REGEXP_DUMP preprocessor definition defined (undocumented). Dump output is directed to stdout, so if the application is not console, it has to be redirected in advance, e.g. into a $(BinaryPath)$(BinaryName)-atlrx.h file.

	CAtlRegExp<> Expression; LPCTSTR pszPattern; BOOL bCaseSensitive;
#if defined(ATL_REGEXP_DUMP)
	REParseError Error = Expression.Parse(pszPattern, bCaseSensitive);
	if(Error != REPARSE_ERROR_OK)
		FILE* pStream = NULL;
			TCHAR pszPath[MAX_PATH] = { 0 };
			ATLVERIFY(GetModuleFileName(_AtlBaseModule.GetModuleInstance(), pszPath, _countof(pszPath)));
			RemoveExtension(pszPath); // ATLPath::
			_tcscat_s(pszPath, _countof(pszPath), _T("-atlrx.txt"));
			ATLVERIFY(freopen_s(&pStream, CStringA(pszPath), "w", stdout) == 0);
		_tprintf(_T("Error %d\n"), Error);
			ATLVERIFY(fclose(pStream) == 0);
		ATLASSERT(FALSE); // Break into debugger
	ATLVERIFY(Expression.Parse(pszPattern, bCaseSensitive) == REPARSE_ERROR_OK);
#endif // defined(ATL_REGEXP_DUMP)

There is also ATLRX_DEBUG definition, which enables other debug capabilities. CAtlRegExp object is given a virtual function OnDebugEvent through which it prints comments on CAtlRegExp::Match process, which can be also redirected to file similar way.

How To: Dump DirectShow media samples

Given a DirectShow filter graph, what media samples are being sent through particular graph point? DumpMediaSamples utility gives a fast answer to this question. It prints out connection media type details (with details of VIDEOINFOHEADER, VIDEOINFOHEADER2 and WAVEFORMATEX structures corresponding to FORMAT_VideoInfo, FORMAT_VideoInfo2 and FORMAT_WaveFormatEx format types) and IMediaSample details obtained through AM_SAMPLE2_PROPERTIES structure. First of all, it is necessary to create a graph of interest using GraphEdit utility. At the point of interest it is necessary to insert [an uninitialized] Sample Grabber Filter with the filter name “SampleGrabber” (this is the default name but if you add second filter which will be given a different name and remove first filter then, the utility would fail). The graph may look like this:


How To: Implement DirectShow Filter using DirectX Media Object DMO (Part 5: In-Place Processing)

Previously on the topic:

Due to the nature of the brightness and constract correction processing, it would make sense to combine and simplify processing to apply correction “in-place”, that is without copying data from input to output buffer, but instead processing the same buffer before it is passed further downstream.

DMO API offers additional optional IMediaObjectInPlace interface to be implemented on the DMO which the hosting object might prefer to regular IMediaObject.

The interface itself is simple with basically the only Process method to actually handle the processing:

// IMediaObjectInPlace
	STDMETHOD(Process)(ULONG nSize, BYTE* pnData, REFERENCE_TIME nStartTime, DWORD nFlags)
	STDMETHOD(Clone)(IMediaObjectInPlace** ppMediaObject)
	STDMETHOD(GetLatency)(REFERENCE_TIME* pnLatencyTime)


How To: Implement DirectShow Filter using DirectX Media Object DMO (Part 4: Merit)

Previously on the topic:

The implemented so far filter/DMO shown a problem related to its unexpectedly high “importance” in the system with the symptom of “auto-insertion” the filter when it is not necessary. For example, let us render an AVI file through Infinite Tee Pin Filter:

The problem is that DirectShow auto-inserts our Brightness/Contrast filter into the graph while it is obviously not expected, wanted or necessary:

The problem is high filter/DMO merit value and a popular YUY2 video format the filter is advertised to accept on input during DMO registration.