FOURCC Codes
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Many digital media formats have FOURCC codes assigned to them. A FOURCC code is a 32-bit unsigned integer that is created by concatenating four ASCII characters. For example, the FOURCC code for YUY2 video is 'YUY2'. For compressed video formats and non-RGB video formats (such as YUV), the biCompression member of the BITMAPINFOHEADER structure should be set to the FOURCC code.
There are various C/C++ macros that make it easier to declare FOURCC values in source code. For example, the MAKEFOURCC macro is declared in Mmsystem.h, and the FCC macro is declared in Aviriff.h. Use them as follows:
DWORD fccYUY2 = MAKEFOURCC('Y','U','Y','2');
DWORD fccYUY2 = FCC('YUY2');
You can also declare a FOURCC code directly as a string literal simply by reversing the order of the characters. For example:
DWORD fccYUY2 = '2YUY'; // Declares the FOURCC 'YUY2'.
Reversing the order is necessary because the Microsoft Windows operating system uses a little-endian architecture. 'Y' = 0x59, 'U' = 0x55, and '2' = 0x32, so '2YUY' is 0x32595559.
Converting FOURCC Codes to Subtype GUIDs
A range of 2*32 GUIDs is reserved for representing FOURCCs. These GUIDs are all of the form XXXXXXXX-0000-0010-8000-00AA00389B71 where XXXXXXXX is the FOURCC code. Thus, the subtype GUID for YUY2 is 32595559-0000-0010-8000-00AA00389B71.
Many of these GUIDs are defined already in the header file Uuids.h. For example, the YUY2 subtype is defined as MEDIASUBTYPE_YUY2. The DirectShow base class library also provides a helper class, FOURCCMap, which can be used to convert FOURCC codes into GUID values. The FOURCCMap constructor takes a FOURCC code as an input parameter. You can then cast the FOURCCMap object to the corresponding GUID:
FOURCCMap fccMap(FCC('YUY2'));
GUID g1 = (GUID)fccMap;
// Equivalent:
GUID g2 = (GUID)FOURCCMap(FCC('YUY2'));
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