John McGowan's AVI Overview: Programming and Other Technical Topics

Windows Multimedia System

In Win16 and Win32, Microsoft created a partially unified system for handling multimedia. This system consists of the high level Media Control Interface or MCI Application Programming Interface (API) and associated MCI drivers. Playback of AVI files can be controlled through the high level MCI API and the MCIAVI.DRV MCI driver. The Windows Multimedia System also provides a number of low level API's such as the WAVE API for waveform audio and associated device drivers such as the WAVE device drivers for sound cards. Under Windows NT 4.0, the MCI and low level API's are stored in the file WINMM.DLL The API's are: MCI (high level API - useful for AVI playback) joy (joystick devices) midi (MIDI devices) mixer (MIXER devices) wave (waveform audio input and output devices) mmio (low level functions to parse RIFF files) time (timers etc.) aux (auxiliary sound device) When a program loads the MCIAVI driver, the Multimedia System has the intelligence to locate and invoke the appropriate MCI driver (MCIAVI.DRV in 16-bit Windows or MCIAVI32.DLL in 32 bit windows) and pass the MCI commands such as MCI_PLAY to the MCI driver. The MCIAVI driver then calls Video for Windows to decompress the video, GDI (or another graphics API) to display the decoded frames, and WAVE to output the decoded audio samples. A dump of the functions exported by winmm.dll under NT 4.0 generated with the Microsoft DUMPBIN.EXE utility follows: Microsoft (R) COFF Binary File Dumper Version 5.00.7022 Copyright (C) Microsoft Corp 1992-1997. All rights reserved. Dump of file winmm.dll File Type: DLL Section contains the following Exports for WINMM.dll 0 characteristics 31EC70B4 time date stamp Tue Jul 16 21:48:52 1996 0.00 version 2 ordinal base 197 number of functions 197 number of names ordinal hint name 3 0 CloseDriver (000026CE) 4 1 DefDriverProc (00005AF4) 5 2 DriverCallback (0000254E) 6 3 DrvGetModuleHandle (00001D37) 7 4 GetDriverModuleHandle (00001D37) 8 5 MigrateAllDrivers (00013E79) 9 6 MigrateMidiUser (00013E60) 10 7 MigrateSoundEvents (00011A3C) 11 8 NotifyCallbackData (0000B2C2) 12 9 OpenDriver (00002036) 13 A PlaySound (00008ACB) 2 B PlaySoundA (00008ACB) 14 C PlaySoundW (00009AE1) 15 D SendDriverMessage (00001000) 16 E WOW32DriverCallback (0000C448) 17 F WOW32ResolveMultiMediaHandle (0000CC3C) 18 10 WOWAppExit (00009D3F) 19 11 aux32Message (0000C507) 20 12 auxGetDevCapsA (0000A3FD) 21 13 auxGetDevCapsW (00008C77) 22 14 auxGetNumDevs (00006AE4) 23 15 auxGetVolume (0000A4A1) 24 16 auxOutMessage (00008BFF) 25 17 auxSetVolume (0000A4C9) 26 18 joy32Message (0000C768) 27 19 joyConfigChanged (0000AE40) 28 1A joyGetDevCapsA (0000A99A) 29 1B joyGetDevCapsW (0000AB40) 30 1C joyGetNumDevs (0000AB96) 31 1D joyGetPos (0000ABAA) 32 1E joyGetPosEx (0000ABFD) 33 1F joyGetThreshold (0000AC5C) 34 20 joyReleaseCapture (0000ACA8) 35 21 joySetCapture (0000ACFC) 36 22 joySetThreshold (0000AE06) 37 23 mci32Message (00007566) 38 24 mciDriverNotify (00007006) 39 25 mciDriverYield (00008727) 40 26 mciExecute (0000D92C) 41 27 mciFreeCommandResource (000035CE) 42 28 mciGetCreatorTask (0000DCD5) 43 29 mciGetDeviceIDA (0000DCA3) 44 2A mciGetDeviceIDFromElementIDA (0000DBC6) 45 2B mciGetDeviceIDFromElementIDW (0000DBF5) 46 2C mciGetDeviceIDW (00005372) 47 2D mciGetDriverData (0000158B) 48 2E mciGetErrorStringA (0000DA46) 49 2F mciGetErrorStringW (0000352F) 50 30 mciGetYieldProc (0000E1F3) 51 31 mciLoadCommandResource (00002A75) 52 32 mciSendCommandA (000015D4) 53 33 mciSendCommandW (000014A1) 54 34 mciSendStringA (00004927) 55 35 mciSendStringW (00004A24) 56 36 mciSetDriverData (000058BD) 57 37 mciSetYieldProc (000034C9) 58 38 mid32Message (0000BDFD) 59 39 midiConnect (0001019E) 60 3A midiDisconnect (0001018C) 61 3B midiInAddBuffer (0001004A) 62 3C midiInClose (0000FF42) 63 3D midiInGetDevCapsA (0000FCCC) 64 3E midiInGetDevCapsW (0000FC71) 65 3F midiInGetErrorTextA (0000FDEB) 66 40 midiInGetErrorTextW (0000FDB2) SetInfo (0000EBF4) 140 8A mmioStringToFOURCCA (0000ED9A) (00008BC5) Under Windows 3.x and Windows 95, the DLL MMSYSTEM.DLL (short for MultiMedia System) contains the multimedia API's. Return to Top

Video for Windows

Video for Windows is an entire system for handling video in Microsoft Windows. It was part of MS Windows 3.1 The original Video for Windows is a collection of 16 bit windows utilities, dynamic link libraries, and other components. The AVI file and file format is a central part of Video for Windows. Microsoft Visual C++ 5.0 has a Video for Windows include file Vfw.h which contains the various API's that make up Video for Windows: * COMPMAN - Installable Compression Manager. * DRAWDIB - Routines for drawing to the display. * VIDEO - Video Capture Driver Interface * * AVIFMT - AVI File Format structure definitions. * MMREG - FOURCC and other things * * AVIFile - Interface for reading AVI Files and AVI Streams * MCIWND - MCI/AVI window class * AVICAP - AVI Capture Window class * * MSACM - Audio compression manager. Microsoft released a Video for Windows 1.0 for Windows 3.1 in November 1992, followed by Video for Windows 1.1. There have been several versions of Video for Windows 1.1 identified by a trailing alphabetical character such as 1.1e The last and most recent version of Video for Windows 1.1 for Windows 3.x is Video for Windows 1.1e This is available by ftp from Microsoft. Microsoft has provided a 32-bit version of Video for Windows for Windows 95, while threatening to replace Video for Windows with ActiveMovie. This version has 32 bit versions of the Video for Windows codecs such as Cinepak. Other DLL's in the Video for Windows 95 are also 32-bit How much of the Video for Windows in Windows 95 is 32 bit code is not clear; many of the codecs are clearly 32 bit codecs. Nor is it clear how much has been changed or modified besides the convesion to 32-bit code. Windows NT 3.5, 3.51 and Windows NT 4.0 include a Video for Windows for NT. Presumably this is strictly 32-bit. It is not clear how much code is shared between the NT Video for Windows and the Windows 95 Video for Windows. Note that hardware device drivers are different between Windows 95 and NT 3.5/3.51/4.0. ActiveMovie 1.0 and DirectShow (formerly ActiveMovie 2.0) are 32-bit successors to Video for Windows for both Windows 95 and Windows NT. These support AVI files. ActiveMovie started out life under the code name Quartz; early Beta releases of ActiveMovie were known as Quartz. ActiveMovie 1.0 is bundled with Windows 95b (OEM Service Release 2.x) and Internet Explorer 3.x/4.x for Windows 95. It can also be downloaded and installed in Windows 95 separately. Note that ActiveMovie 1.0 does NOT completely replace Video for Windows. For example, ActiveMovie 1.0 does not provide a video capture mechanism. Video capture still uses Video for Windows capture drivers. ActiveMovie 1.0 is a 32 bit software component that can run in NT's user mode. It runs under Windows NT 4.0 as well as Windows 95. DirectShow (ActiveMovie 2.0) will supposedly add a number of new features including video capture support, kernel mode streaming, and miscellaneous other features. VIDEO FOR WINDOWS under WINDOWS NT 4.0 Under NT 4.0, Video for Windows is implemented as a collection of 32-bit DLL's in the Microsoft 32-bit Common Object File Format or COFF format. These are usually located in the \WINNT\SYSTEM32 directory where Windows NT stores most of the system DLL's, drivers, and so forth. MSVFW32.DLL ( Microsoft Video for Windows DLL - NT 4.0 ) AVIFIL32.DLL ( AVIFILE API for Reading and Writing AVI Files and Streams ) AVICAP32.DLL ( AVI Capture Window Class ) MCIAVI32.DLL ( Video for Windows MCI Driver ) MSACM32.DRV ( Microsoft Audio Compression Manager ) MSACM32.DLL ( more Microsoft Audio Compression Manager ) MSRLE32.DLL ( Microsoft RLE Video Codec ) IR32_32.DLL ( Intel Indeo 3.2 Video Codec ) MSVIDC32.DLL ( Microsoft Video 1 Codec ) ICCVID.DLL ( Cinepak for Windows 32 - Radius ) What is in MSVFW32.DLL? MSVFW32.DLL includes the DRAWDIB, Installable Compression Manager or ICM, and MCI Windows components of Video for Windows. Other components are stored in other DLL's. This is a dump of the functions exported by MSVFW32.DLL Version 4.00 Microsoft (R) COFF Binary File Dumper Version 5.00.7022 Copyright (C) Microsoft Corp 1992-1997. All rights reserved. Dump of file msvfw32.dll File Type: DLL Section contains the following Exports for MSVFW32.dll 0 characteristics 31EC70E9 time date stamp Tue Jul 16 21:49:45 1996 0.00 version 2 ordinal base 47 number of functions 47 number of names ordinal hint name 3 0 DrawDibBegin (00001E14) 4 1 DrawDibChangePalette (00008C30) 5 2 DrawDibClose (0000888A) 6 3 DrawDibDraw (000010A6) 7 4 DrawDibEnd (00008BEC) 8 5 DrawDibGetBuffer (00008EFC) 9 6 DrawDibGetPalette (00002F97) 10 7 DrawDibOpen (00003E0A) 11 8 DrawDibProfileDisplay (00003EBA) 12 9 DrawDibRealize (00001D49) 13 A DrawDibSetPalette (00001C0D) 14 B DrawDibStart (00002EEB) 15 C DrawDibStop (00002F42) 16 D DrawDibTime (00008C2B) 17 E GetOpenFileNamePreview (0000C7DC) 18 F GetOpenFileNamePreviewA (0000C7DC) 19 10 GetOpenFileNamePreviewW (0000C6A5) 20 11 GetSaveFileNamePreviewA (0000C7EC) 21 12 GetSaveFileNamePreviewW (0000C7CC) 22 13 ICClose (000035E0) 23 14 ICCompress (00004CE5) 24 15 ICCompressorChoose (00005F61) 25 16 ICCompressorFree (00005615) 26 17 ICDecompress (00004D4B) 27 18 ICDraw (0000106A) 28 19 ICDrawBegin (00001B95) 29 1A ICGetDisplayFormat (00004D8E) 30 1B ICGetInfo (00004C60) 31 1C ICImageCompress (00005A96) 32 1D ICImageDecompress (00005D2A) 33 1E ICInfo (00002FEB) 34 1F ICInstall (00004574) 35 20 ICLocate (0000372E) 36 21 ICMThunk32 (0000841C) 37 22 ICOpen (0000337C) 38 23 ICOpenFunction (00003B53) 39 24 ICRemove (0000488B) 40 25 ICSendMessage (00001000) 41 26 ICSeqCompressFrame (000059A7) 42 27 ICSeqCompressFrameEnd (00005907) 43 28 ICSeqCompressFrameStart (000056E4) 44 29 MCIWndCreate (0000C988) 45 2A MCIWndCreateA (0000C988) 46 2B MCIWndCreateW (0000C8CC) 47 2C MCIWndRegisterClass (0000C83F) 48 2D StretchDIB (00009D13) 2 2E VideoForWindowsVersion (000041D1) Summary 8000 .data 3000 .rdata 2000 .reloc 3000 .rsrc 11000 .text VIDEO FOR WINDOWS FOR WINDOWS 95 Microsoft distributed a new Video for Windows for Windows 95 while emphasizing Quartz/ActiveMovie/DirectShow in its marketing. Video for Windows 95 Files MSRLE32.DLL (32-bit Microsoft RLE Video Codec) IR32_32.DLL (32-bit Indeo 3.2 Video Codec) ICCVID.DLL (32-bit Radius Cinepak Video Codec) MSVIDC32.DLL (32-bit Microsoft Video 1 Video Codec ) MSVIDEO.DLL (16-bit Video for Windows DLL) MCIAVI.DRV (16-bit AVI Video MCI Driver) AVIFILE.DLL (16-bit AVIFILE) AVICAP.DLL (16-bit AVICAP) AVICAP32.DLL (32-bit AVICAP) MSVFW32.DLL (32-bit Video for Windows DLL - with VfW API) AVIFIL32.DLL (32-bit AVIFILE) SUMMARY Video for Windows 1.0 (Windows 3.x) Video for Windows 1.1 (a-e) (Windows 3.x) Video for Windows (Windows 95 - has 32-bit codecs and other 32-bit DLL's) Video for Windows (Windows NT 3.5, 3.51, and 4.0) Quartz (Betas of ActiveMovie) (Windows 95) ActiveMovie 1.0 (Windows 95 and NT 4.0) ActiveMovie 2.0 (DirectShow) (probably Windows 97/98/Memphis and NT 5.0) Return to Top


The Microsoft Windows audio (sound) input/output system, commonly referred to as Wave or WAVE, predates Video for Windows, which is wrapped around WAVE in various ways. The audio tracks in AVI files are simply waveform audio (or WAV) data used by the wave system. Video for Windows parses the AVI files, extracts the WAV data, and pipes the WAV data to the WAVE system. Video for Windows handles the video track if present. Traditionally, audio input and output devices such as Sound Blaster Cards have a WAVE audio input/output driver to play WAV (waveform audio) files. The simplest waveform audio files consists of a header followed by Pulse Coded Modulation (PCM) sound data, usually uncompressed 8 or 16 bit sound samples. WAVE also provides a mechanism for audio codecs. See elsewhere in the AVI Overview for further information on audio codecs and audio compression. WAVE is present in Windows 3.1 and Windows 95. A different WAVE system is present in Windows NT 3.5, 3.51, and 4.0 At least the hardware device drivers for sound cards must be different in NT. ActiveMovie appears to be replacing WAVE. Return to Top

What is the AVI File Format?

AVI Files are a special case of RIFF files. RIFF is the Resource Interchange File Format. This is a general purpose format for exchanging multimedia data types that was defined by Microsoft and IBM during their long forgotten alliance. Kevin McKinnon writes: In fact, RIFF is a clone of the IFF format invented by Electronic Arts in 1984. They invented the format for Deluxe Paint on the Amiga, and IFF quickly became the standard for interchange on that platform, maintained eventually by Commodore right up 'til it's demise. EA also ported Deluxe Paint to the PC platform and brought IFF with it. IFF even used the 4-character headers (FourCC), though at the time it was simply called a LONGWORD that some clever people decided to pair into four charcter because they looked good in #define's. ;) RIFF is so close to IFF that the good IFF parser routines will (mostly) correctly parse RIFF files. ----End of Kevin---- Further information on the IFF format is available at:

RIFF Files

RIFF files are built from (1) RIFF Form Header 'RIFF' (4 byte file size) 'xxxx' (data) where 'xxxx' identifies the specialization (or form) of RIFF. 'AVI ' for AVI files. where the data is the rest of the file. The data is comprised of chunks and lists. Chunks and lists are defined immediately below. (2) A Chunk (4 byte identifier) (4 byte chunk size) (data) The 4 byte identifier is a human readable sequence of four characters such as 'JUNK' or 'idx1' (3) A List 'LIST' (4 byte list size) (4 byte list identifier) (data) where the 4 byte identifier is a human readable sequence of four characters such as 'rec ' or 'movi' where the data is comprised of LISTS or CHUNKS.

AVI File Format

AVI is a specialization or "form" of RIFF, described below: 'RIFF' (4 byte file length) 'AVI ' // file header (a RIFF form) 'LIST' (4 byte list length) 'hdrl' // list of headers for AVI file The 'hdrl' list contains: 'avih' (4 byte chunk size) (data) // the AVI header (a chunk) 'strl' lists of stream headers for each stream (audio, video, etc.) in the AVI file. An AVI file can contain zero or one video stream and zero, one, or many audio streams. For an AVI file with one video and one audio stream: 'LIST' (4 byte list length) 'strl' // video stream list (a list) The video 'strl' list contains: 'strh' (4 byte chunk size) (data) // video stream header (a chunk) 'strf' (4 byte chunk size) (data) // video stream format (a chunk) 'LIST' (4 byte list length) 'strl' // audio stream list (a list) The audio 'strl' list contains: 'strh' (4 byte chunk size) (data) // audio stream header (a chunk) 'strf' (4 byte chunk size) (data) // audio stream format (a chunk) 'JUNK' (4 byte chunk size) (data - usually all zeros) // an OPTIONAL junk chunk to align on 2K byte boundary 'LIST' (4 byte list length) 'movi' // list of movie data (a list) The 'movi' list contains the actual audio and video data. This 'movi' list contains one or more ... 'LIST' (4 byte list length) 'rec ' // list of movie records (a list) '##wb' (4 byte chunk size) (data) // sound data (a chunk) '##dc' (4 byte chunk size) (data) // video data (a chunk) '##db' (4 byte chunk size) (data) // video data (a chunk) A 'rec ' list (a record) contains the audio and video data for a single frame. '##wb' (4 byte chunk size) (data) // sound data (a chunk) '##dc' (4 byte chunk size) (data) // video data (a chunk) '##db' (4 byte chunk size) (data) // video data (a chunk) The 'rec ' list may not be used for AVI files with only audio or only video data. I have seen video only uncompressed AVI files that did not use the 'rec ' list, only '00db' chunks. The 'rec ' list is used for AVI files with interleaved audio and video streams. The 'rec ' list may be used for AVI file with only video. ## in '##dc' refers to the stream number. For example, video data chunks belonging to stream 0 would use the identifier '00dc'. A chunk of video data contains a single video frame. Alexander Grigoriev writes ... John, ##dc chunk was intended to keep compressed data, whereas ##db chunk nad(sic) to be used for uncompressed DIBs (device independent bitmap), but actually they both can contain compressed data. For example, Microsoft VidCap (more precisely, video capture window class) writes MJPEG compressed data in ##db chunks, whereas Adobe Premiere writes frames compressed with the same MJPEG codec as ##dc chunks. ----End of Alexander The ##wb chunks contain the audio data. The audio and video chunks in an AVI file do not contain time stamps or frame counts. The data is ordered in time sequentially as it appears in the AVI file. A player application should display the video frames at the frame rate indicated in the headers. The application should play the audio at the audio sample rate indicated in the headers. Usually, the streams are all assumed to start at time zero since there are no explicit time stamps in the AVI file. The lack of time stamps is a weakness of the original AVI file format. The OpenDML AVI Extensions add new chunks with time stamps. Microsoft's ASF (Advanced or Active Streaming Format), which Microsoft claims will replace AVI, has time stamp "objects". In principle, a video chunk contains a single frame of video. By design, the video chunk should be interleaved with an audio chunk containing the audio associated with that video frame. The data consists of pairs of video and audio chunks. These pairs may be encapsulated in a 'REC ' list. Not all AVI files obey this simple scheme. There are even AVI files with all the video followed by all of the audio; this is not the way an AVI file should be made. The 'movi' list may be followed by: 'idx1' (4 byte chunk size) (index data) // an optional index into movie (a chunk) The optional index contains a table of memory offsets to each chunk within the 'movi' list. The 'idx1' index supports rapid seeking to frames within the video file. The 'avih' (AVI Header) chunk contains the following information: Total Frames (for example, 1500 frames in an AVI) Streams (for example, 2 for audio and video together) InitialFrames MaxBytes BufferSize Microseconds Per Frame Frames Per Second (for example, 15 fps) Size (for example 320x240 pixels) Flags The 'strh' (Stream Header) chunk contains the following information: Stream Type (for example, 'vids' for video 'auds' for audio) Stream Handler (for example, 'cvid' for Cinepak) Samples Per Second (for example 15 frames per second for video) Priority InitialFrames Start Length (for example, 1500 frames for video) Length (sec) (for example 100 seconds for video) Flags BufferSize Quality SampleSize For video, the 'strf' (Stream Format) chunk contains the following information: Size (for example 320x240 pixels) Bit Depth (for example 24 bit color) Colors Used (for example 236 for palettized color) Compression (for example 'cvid' for Cinepak) For audio, the 'strf' (Stream Format) chunk contains the following information: wFormatTag (for example, WAVE_FORMAT_PCM) Number of Channels (for example 2 for stereo sound) Samples Per Second (for example 11025) Average Bytes Per Second (for example 11025 for 8 bit sound) nBlockAlign Bits Per Sample (for example 8 or 16 bits) Each 'rec ' list contains the sound data and video data for a single frame in the sound data chunk and the video data chunk. Other chunks are allowed within the AVI file. For example, I have seen info lists such as 'LIST' (4 byte list size) 'INFO' (chunks with information on video) These chunks that are not part of the AVI standard are simply ignored by the AVI parser. AVI can be and has been extended by adding lists and chunks not in the standard. The 'INFO' list is a registered global form type (across all RIFF files) to store information that helps identify the contents of a chunk. The sound data is typically 8 or 16 bit PCM, stereo or mono, sampled at 11, 22, or 44.1 KHz. Traditionally, the sound has typically been uncompressed Windows PCM. With the advent of the WorldWide Web and the severe bandwidth limitations of the Internet, there has been increasing use of audio codecs. The wFormatTag field in the audio 'strf' (Stream Format) chunk identifies the audio format and codec.

OpenDML AVI File Format Extensions

The Open Digital Media (OpenDML) Consortium has defined an OpenDML AVI File Format Extensions which extend AVI to support a variety of features required for professional video production. These include support for fields (not just frames), file sizes larger than 1 GB, timecodes, and many other features. Microsoft has reportedly incorporated OpenDML AVI support in DirectShow 5.1 (ActiveMovie 5.1). It is also used by various professional video applications for the PC, in particular Matrox's DigiSuite software. The Open Digital Media Consortium AVI File Format Extensions add new lists and chunks to the AVI file which contain extra data such as timecodes not incorporated in the original AVI standard. OpenDML appears to have been spearheaded by Matrox to improve AVI for professional video authoring and editing. Matrox makes a variety of PC video products such as DigiSuite for professional and broadcast video authoring and editing. The OpenDML AVI File Format Extensions are primarily for the Motion JPEG AVI files used for professional video authoring and editing. The OpenDML effort seems to have been pushed to one side with the advent of ActiveMovie, NetShow, Advanced (formerly Active) Streaming Format (ASF) Files, and other Microsoft initiatives. On Oct. 2, 1997, the OpenDML AVI File Format Extensions Version 1.02 specification document (dated February 28, 1996) was available at the Matrox Electronic Systems, Ltd. Web site at: The specification is in Adobe Portable Document Format (PDF). Since Matrox seems to rearrange their site from time to time and one can't always find the specification, I've included a link to a copy of the PDF version of the specification on my Web site. PDF OpenDML AVI File Format Extensions Specification Document Get Adobe Acrobat Reader (PDF Viewer)

Where to get the exact AVI specification?

Microsoft Visual C++ 5.0 has a Video for Windows include file Vfw.h which gives the exact AVI data structures such as the various headers used in AVI files. The file also has comments explaining the structure of the AVI file. Video for Windows refers to the AVI Format by the mnemonic AVIFMT. At one time, the format information was apparently stored in an AVIFMT.H header file. The format information now appears consolidated in Vfw.h In addition to the Video for Windows header files, Chapter Four of the Video for Windows Programmer's Guide, "AVI Files", gives a detailed specification of the AVI file format. Return to Top

AVI and Windows Bitmaps (DDB, DIB, ...)

Microsoft Windows represents bitmapped images internally and in files as Device Dependent Bitmaps (DDB), Device Independent Bitmaps (DIB), and DIB Sections. Uncompressed 'DIB ' AVI files represent video frames as DIB's. Various multimedia API's that work with AVI use Windows bitmapped images. Prior to Windows 3.0, Windows relied on Device Dependent Bitmaps for bitmapped images. A DDB is stored in a format understood by the device driver for a particular video card. As the name suggests, DDB's are not generally portable. The structure of a DDB is: typedef struct tagBITMAP { // bm LONG bmType; /* always zero */ LONG bmWidth; /* width in pixels */ LONG bmHeight; /* height in pixels */ LONG bmWidthBytes; /* bytes per line of data */ WORD bmPlanes; /* number of color planes */ WORD bmBitsPixel; /* bits per pixel */ LPVOID bmBits; /* pointer to the bitmap pixel data */ } BITMAP; Usually the pixel data immediately follows the BITMAP header. (BITMAP header)(Pixel Data) The HBITMAP handles used by GDI are handles to Device Dependent Bitmaps. The GDI function BitBlt and StretchBlt are actually using Device Dependent Bitmaps. With Windows 3.0, Microsoft introduced the Device Independent Bitmap or DIB, the reigning workhorse of bitmapped images under Windows. The DIB provided a device independent way to represent bitmapped images, both monochrome and color. Windows retains DDB's despite the introduction of the DIB. For example, to use a DIB, you might call: hBitmap = CreateDIBitmap(...) CreateDIBitmap creats a DDB from a DIB, returning the GDI HBITMAP handle of the DDB for further GDI calls. At a low level, Windows and GDI are still using DDB's. The DIB files have a standard header that identifies the format, size, color palette (if applicable) of the bitmapped image. The header is a BITMAPINFO structure. typedef struct tagBITMAPINFO { BITMAPINFOHEADER bmiHeader; RGBQUAD bmiColors[1]; } BITMAPINFO; The BITMAPINFOHEADER is a structure of the form: typedef struct tagBITMAPINFOHEADER{ // bmih DWORD biSize; LONG biWidth; LONG biHeight; WORD biPlanes; WORD biBitCount DWORD biCompression; /* a DIB can be compressed using run length encoding */ DWORD biSizeImage; LONG biXPelsPerMeter; LONG biYPelsPerMeter; DWORD biClrUsed; DWORD biClrImportant; } BITMAPINFOHEADER; bmiColors[1] is the first entry in an optional color palette or color table of RGBQUAD data structures. True color (24 bit RGB) images do not need a color table. 4 and 8 bit color images use a color table. typedef struct tagRGBQUAD { // rgbq BYTE rgbBlue; BYTE rgbGreen; BYTE rgbRed; BYTE rgbReserved; /* always zero */ } RGBQUAD; A DIB consists of (BITMAPINFOHEADER)(optional color table of RGBQUAD's)(data for the bitmapped image) A Windows .BMP file is a DIB stored in a disk file. .BMP files prepend a BITMAPFILEHEADER to the DIB data structure. typedef struct tagBITMAPFILEHEADER { // bmfh WORD bfType; /* always 'BM' */ DWORD bfSize; /* size of bitmap file in bytes */ WORD bfReserved1; /* always 0 */ WORD bfReserved2; /* always 0 */ DWORD bfOffBits; /* offset to data for bitmap */ } BITMAPFILEHEADER; Structure of Data in a .BMP File (BITMAPFILEHEADER)(BITMAPINFOHEADER)(RGBQUAD color table)(Pixel Data) The Win32 API documentation from Microsoft provides extensive information on the data structures in a DIB. In Windows 95 and Windows NT, Microsoft added the DIBSection to provide a more efficient way to use DIB's in programs. The DIBSection was originally introduced in Windows NT to reduce the number of memory copies during blitting (display) of a DIB. Return to Top


Active Movie is a new multimedia architecture for Windows 95 and Windows NT (4.0 and after). ActiveMovie includes support for playing AVI, QuickTime (.MOV), and MPEG files. ActiveMovie is apparently intended to supersede Video for Windows. ActiveMovie 1.0 ships with the OEM Service Release 2 (OSR2) of Windows 95. It did not ship with prior releases of Windows 95 but was available separately through the ActiveMovie SDK. ActiveMovie 1.0 is also bundled with Microsoft's Internet Explorer for Windows 95 and NT 4.0 Internet Explorer can be downloaded from the Microsoft Web site at: Active Movie 1.0 can be downloaded by itself from the Microsoft Internet Explorer site. (6/6/97) ActiveMovie 1.0 appears to be a 32 bit software component that runs under both Windows 95 and Windows NT 4.0 user mode. ActiveMovie provides at least three different programming interfaces: - The ActiveMovie ActiveX Control - ActiveMovie Component Object Model (COM) interfaces - The OM-1 MPEG MCI (Media Control Interface) command set Amongst other things, the ActiveMovie ActiveX Control can be embedded in HTML Web pages and programmed via VBScript or JavaScript. It can also be programmed using Visual C++ or Visual Basic as part of applications. The ActiveMovie COM interaces can be accessed through Visual C++ or Visual Basic. ActiveMovie supports a subset of the Media Control Interface (MCI) commands familiar to Video for Windows programmers. These commands can be accessed through the mciSendCommand(...) and mciSendString(...) functions in C/C++. ActiveMovie 1.0 does NOT provide video capture. Windows 95 with ActiveMovie 1.0 continues to use the Video for Windows video capture system and drivers. ActiveMovie 2.0 (renamed DirectShow in 1997) will provide a new, alternative mechanism for video capture. According to information distributed by Microsoft at the WDM Device Driver Conference in April, 1997, ActiveMovie 2.0 will use the WDM Stream Class under Memphis (formerly Windows 97) and Windows NT 5.0 to implement video capture. This is subject to possible change since neither Memphis nor NT 5.0 has been released (7/27/97). Extensive information on ActiveX and ActiveMovie is available at the Microsoft Web site. ActiveMovie 1.0 SDK Documentation at (6/28/97): v1doc/ Return to Top

GUID's and AVI

GUID stands for Global Unique IDentifier. In Microsoft's Component Object Model (COM) morass, an object oriented programming model that incorporates MFC (Microsoft Foundation Classes), OLE (Object Linking Embedding), ActiveX, ActiveMovie and everything else Microsoft is hawking lately, a GUID is a 16 byte or 128 bit number used to uniquely identify objects, data formats, everything. Within ActiveMovie, there are GUID's for video formats, corresponding to the FOURCC's or Four Character Codes used in Video for Windows. These are specified in the file uuids.h in the Active Movie Software Developer Kit (SDK). ActiveMovie needs to pass around GUID's that correspond to the FOURCC for the video in an AVI file. With proper programming, this should be hidden from end users but ActiveMovie programmers need to know about GUID's. Return to Top

What are the GUIDs for the Video for Windows Codecs?

Video for Windows codecs are identified by a thirty-two bit Four Character Code (FOURCC). A Four Character Code is a thirty-two bit value formed from the ASCII codes for four characters. Typically, the four characters are a memnonic for the item identified. For example, the popular Cinepak video codec is 'CVID'. Microsoft has introduced 128-bit (16 byte) Globally Unique Identifiers (GUIDs) for identifying everything in the Microsoft Universe. Microsoft has established a mapping procedure from the human readable Four Character Codes to GUIDs for video codecs. Replace the "x"'s in the GUID below with the 32-bit value built from the Four Character Code. The Four Character Code is in 7-bit ASCII. xxxxxxxx-0000-0010-8000-00AA00389B71 For example, the GUID for Radius Cinepak is: 44495643-0000-0010-8000-00AA00389B71 44 is the hexadecimal (base 16) ASCII code for 'D' 49 is the hexadecimal (base 16) ASCII code for 'I' 56 is the hexadecimal (base 16) ASCII code for 'V' 43 is the hexadecimal (base 16) ASCII code for 'C' Note that the order of the characters is reversed from naive expectation. Return to Top


DirectShow is Microsoft's new name for ActiveMovie 2.0 Microsoft has shifted to marketing ActiveMovie as an integral part of DirectX. Apparently DirectShow (ActiveMovie 2.0) will be released to the general public as part of Direct X 5.0. Return to Top


DirectDraw, one of the components of DirectX, is a new Applications Programming Interface (API) that is part of Windows 95 and Windows NT 4.0. DirectDraw allows programs to directly access video memory and other hardware features in video display cards. Direct Draw also defines new device drivers for graphic/video display adapters to supersede the GDI display drivers. DirectDraw needs the new device drivers. DirectDraw consists of a new API and new hardware drivers known as the Direct Draw Hardware Abstraction Layer (HAL). In the Windows 3.1 Graphic Device Interface (GDI), an application program never writes directly to the memory in a display card. It writes to a buffer in main memory within Windows. GDI invokes a GDI video device driver and copies the image from main memory to the video memory of the video card. This multiple copying of the image inevitably slows down the display. The DirectDraw API provides a mechanism allowing appliation programs to write directly into the video card's memory. It also provides a mechanism to access various special features in video cards such as color space conversion, hardware scaling, z-buffering, alpha blending, and so forth. Video card manufacturers must provide a DirectDraw driver for DirectDraw to work with their card. Microsoft's ActiveMovie uses DirectDraw to achieve faster playback of AVI, QuickTime, and MPEG files. There is extensive information on the DirectDraw and DirectX API's at the Microsoft Web site. The DirectX 3 SDK can be downloaded from the Microsoft Developer Online Web site (6/28/97): Select Microsoft SDKs from the Technical Information section, or point your browser at: Versions of DirectX - DirectX 1 - DirectX 2 - DirectX 3 - DirectX 3A (latest as of 2/18/97) - DirectX 5.0 (in development?) - DirectX 6.0 (mentioned occasionally by Microsoft) Return to Top

What is a driver?

Most often, driver refers to a software component that handles control and communication with hardware in a computer. Most but not all hardware device drivers run in a privileged mode such as the Ring Zero mode of the Intel 80x86 processors. Microsoft Windows uses the term driver to refer to several different software components. - Hardware Device Drivers - Windows 3.x or 95 Virtual Device Drivers (VxD's) - not all VxD's access hardware - Microsoft Windows Installable Drivers such as - Media Control Interface or MCI Drivers - Video for Windows Codecs (Compressor/Decompressors) - Audio Codecs (Compressor/Decompressors) Hardware Device Drivers include MS-DOS device drivers, DOS Terminate and Stay Resident Programs that access hardware, Windows 3.x and 95 VxD's (Virtual Device Drivers) that access hardware, Windows DLL's that access hardware but do not run in Ring Zero, Windows NT kernel-mode device drivers, and the new Win32 Driver Model (WDM) drivers for Memphis/Windows 98 and NT 5.0 Microsoft Windows Installable Drivers are Ring Three (Windows 95) or user-mode (Windows NT) Dynamic Link Libraries (DLL's) with a single entry point DriverProc(). MCI drivers, Video for Windows Codecs, Microsoft Audio Compression Manager Codecs, and a variety of other software components are Installable Drivers. Some installable drivers are hardware drivers. Return to Top

GDI Device Drivers

In Windows 3.1, and to a lesser extent Windows 95, the Graphic Device Interface or GDI is the system that handles graphic display, including putting bitmaps on the display monitor. Amongst other things, GDI defines a set of GDI functions that application programs call such as BitBlt(...) to display graphics on the screen. GDI also controls printers and other graphic output devices. Windows NT also provides a GDI system, but the underlying hardware device drivers are different. Windows 3.1 GDI drivers won't work under NT. Application programs written using the GDI API will usually work under NT. GDI is device independent. To achieve this, GDI uses GDI device drivers loaded dynamically as needed. The most commonly used GDI device driver is the DISPLAY device (for display monitors). In Windows 3.1, this is specified by lines such as: display.drv=SUPERVGA.DRV in the SYSTEM.INI file. SUPERVGA.DRV is a generic super vga graphic display adapter driver shipped with Windows 3.1 SUPERVGA.DRV is a GDI Device Driver The printer driver is another common GDI device driver. In Windows 3.1 or Windows 95 without DirectDraw, GDI handles display of video frames on the display monitor. GDI defines a set of standard functions exported by GDI Device Drivers. A GDI Device Driver can also report that it does not support a particular function. Standard Functions for GDI Device Driver Entry Name Description 01 BitBlt Transfer bits from src (source) to dest (destination) rect (rectangle) 02 ColorInfo Converts between logical and physical colors. . . . 30 BitmapBits Sets, retrieves, copies bitmap data. Video card manufacturers write and provide GDI Device Drivers for video cards. When Video for Windows plays an AVI file, Video for Windows usually uses the Media Control Interface (MCI) driver for AVI files (MCIAVI.DRV). The MCI driver will call GDI to display each decoded frame of video and WAVE to output the decoded audio to the sound card. In Windows 95 or NT 4.0, ActiveMovie 1.0 has "renderers" which can invoke GDI or DirectDraw depending on the situation to display the decoded video frames. There are also audio renderers to output the decoded audio from an AVI, QuickTime, or MPEG file. Return to Top

Direct Draw Hardware Abstraction Layer

DirectDraw is a replacement for GDI for Windows 95 and Windows NT 4.0. See elsewhere in this overview for sections on GDI and DirectDraw. The Direct Draw Hardware Abstraction Layer (HAL) defines Direct Draw device drivers for graphics/video display adapters. Graphics and video card manufacturers provide DirectDraw device drivers. For Direct Draw to work it must have these device drivers. DirectDraw also defines a DirectDraw Applications Programming Interface (API), a standard set of function calls invoked by applications. The DirectDraw API in turn calls the Direct Draw HAL to access the graphics/video display adapter. ActiveMovie can invoke DirectDraw for video output under Windows 95 and Windows NT 4.0. Return to Top

Virtual Device Drivers

In Windows 3.x and Windows 95, Virtual Device Drivers or VXD's are usually the hardware device drivers. They run in a privileged mode of the Intel 80x86 processor known as Ring Zero. Video display adapters and video capture cards usually have an associated VXD written by the card or chip manufacturer. Note that some Windows device drivers are implemented as Dynamic Link Libraries (DLL's) that do not run in the privileged, Ring Zero, mode of the 80x86 processor or as MS-DOS programs that access hardware. These device drivers are not VXD's. There are some things that only VXD's can do. Most PC hardware, especially with high bandwidth requirements, use VXD's. Device drivers for video display adapters are rarely a single VXD. Often the Device Driver Interface (DDI) is implemented as a Dynamic Link Library which does not run at Ring Zero. Only parts of the device driver that need to run at Ring Zero are in the VXD. A full video display device driver is often built of several files, frequently including one or more VXDs. VXD's are usually found in the \WINDOWS\SYSTEM directory. VXD's will not work for hardware under Windows NT 3.51 or NT 4.0 Windows NT has its own Windows NT Driver Model for device drivers. In "Memphis", formerly Windows 97, and NT 5.0, Microsoft is attempting to provide a common driver model known as WDM or Win32 Driver Model so that the same drivers can be used in both Memphis and NT. Return to Top

Windows NT Driver Model

Windows NT (3.51, 4.0) has its own system of hardware device drivers. While NT can often run Windows 3.x and Windows 95 applications, NT cannot use Windows 3.x or Windows 95 device drivers (the Virtual Device Drivers or VxD's). For most people working with AVI, or video in general, the main point to remember is that different drivers are needed for NT than Windows 95 (or Windows 3.x). Most hardware manufacturers provide both Windows 3.x, 95, and NT drivers. TOOLS Programmers will need the Windows NT DDK (Device Driver Kit) to develop Windows NT drivers. This is available in a subscription to Microsoft Developer Network (Professional). Return to Top

Win32 Driver Model (WDM)

The Win32 Driver Model (WDM) is a new device driver system for Memphis (formerly Windows 97) and Windows NT 5.0 The notion is that the same device drivers will work under both Memphis and NT 5.0 WDM is largely the Windows NT Driver Model used in NT 3.51 and 4.0 It is still under development. Video display card and video capture card companies will presumably be providing WDM drivers for Memphis and NT 5.0 in the future. Memphis is supposed to be backward compatible so that Windows 95 Device Drivers will still work under Memphis. Similarly, NT 4.0 Device Drivers will still work under NT 5.0 A WDM Device Driver will work under both Memphis and NT 5.0. Return to Top


MMX or Multimedia Extensions to the Pentium instruction set are 57 new instructions that accelerate some graphics, imaging, and multimedia operations. Multimedia often involves small data types such as 8 bit or 16 bit pixels that can be processed in parallel. For example, in principle, a 32 bit instruction could operate of four 8 bit pixels in parallel. A simple example would be adding four 8 bit pixels in parallel. The MMX instructions add clipping for underflow and overflow situations. 255 0 0 255 Normal addition of four 8 bit pixels backed in 32 bits + 0 0 0 255 ------------- 255 0 1 0 255 0 0 255 MMX style clipping of overflow + 0 0 0 255 -------------- 255 0 0 255 Intel developed the MMX instructions and added them to recent versions of the Pentium chip known as the P55C or Pentium with MMX. The MMX instructions were also added to the Pentium Pro. The Pentium Pro with MMX was code named Klamath, but called the Pentium II when actually shipped in 1997. MMX can accelerate various graphics and multimedia operations. It can accelerate video codecs. In particular, the block Discrete Cosine Transform used in JPEG, Motion JPEG, H.261, H.263, H.263+, MPEG-4, MPEG-1, and MPEG-2 can be accelerated using MMX instructions. Initially compilers have not supported generation of MMX instructions, so critical portions of the multimedia algorithms must be hand-coded in Pentium assembler using the MMX instructions. An MMX version of a codec may be able to encode and decode an AVI file (for example) faster on a PC with MMX. DOCUMENTATION ON MMX Further information on MMX is available at the Intel Web site for developers: Click on the Literature Center link, then select "Pentium Processor with MMX" from the pull down list of products. This information is dated August 1, 1997. The Intel Web site changes from time to time. In addition to various on-line documentation at the Web site, Intel has some manuals on MMX: Intel Architecture MMX Technology Developers Manual (Order No. 243013) Intel Architecture MMX Technology Programmer's Reference Manual (Order No. 243007) TOOLS FOR WORKING WITH MMX Intel provides an MMX Technology Macro Package for use with the Microsoft Macro Assembler (MASM). This can be downloaded from: Intel markets an Intel C/C++ compiler plug-in for Microsoft Visual C/C++ 4.x/5.0. This plug-in includes "special compiler intrinsics" to support MMX. These allow a programmer to use the call syntax of C functions instead of manually coding in assembly language. Example of an "intrinsic" __m64 _m_pmaddwd(__m64 m1, __m64 m2) The Intel C/C++ compiler plug-in is available on the VTune CD-ROM. VTune is discussed below. Intel markets a product called the VTune (TM) Performance Analyzer for profiling programs on the Intel architecture at the machine instruction level. VTune includes support for the MMX instructions and has been used to profile and optimize MMX code. The VTune CD-ROM includes a number of other Intel freebies and products such as the Intel C/C++ compiler plug-in that may be useful developing MMX software. Return to Top


NOTE: ActiveX is NOT ActiveMovie. There is an ActiveMovie ActiveX control, but ActiveX is far more than this. ActiveX is a stripped down version of OLE (Object Linking and Embedding) targetted for the World Wide Web. An ActiveX component or control is a software component written in Visual Basic, Visual C++, or Java that conforms to the ActiveX API. This API is a variant of OLE, designed to create small objects that can be dowloaded over the Internet. An ActiveX object or control may reside on a Web page to be downloaded and run when Microsoft's Internet Explorer views the page. An ActiveX control can be the ActiveMovie ActiveX control which plays AVI and other video formats supported by ActiveMovie. An ActiveX control can be an entertaining animation, a game like tic tac toe, anything. In this sense, ActiveX objects are similar to Java applets. Unlike Java applets, once an ActiveX control has been downloaded once it remains on the downloading machine and can be used again without being dowloaded again. Also unlike Java, ActiveX controls are tied to a particular architecture, Windows 95 or Windows NT. It is not clear how much support Microsoft will give for ActiveX on non-Windows platforms. Java applets are compiled to a Java bytecode that will run on any platform with a Java virtual machine implemented. Java applets will run on Windows 3.1, Windows 95, Windows NT, PowerMacintosh, Linux, Sun, and various other Unix platforms. There is extensive information on ActiveX at the Microsoft Web site. The ActiveX SDKs can be downloaded from the Microsoft Developer Online Web Site (6/28/97): Select Microsoft SDKs from the Technical Information section or point your browser at: Netscape Fans: ScriptActive is a Netscape Plug-In that adds support for ActiveX to Netscape. ScriptActive Web Site Return to Top

Playing an AVI File within a Windows Application

Programmers can play an AVI File within a Windows application by several means. The simplest traditional way is to use the Media Control Interface (MCI). Video for Windows includes an MCI driver mciavi.drv for AVI files. Within the Windows API, programmers can use two C language API functions, mciSendString(...) and mciSendCommand(...), to communicate with the MCI driver. mciSendString(...) sends MCI command strings such as "play from 0 to 100" to the MCI driver. mciSendCommand(...) sends MCI command messages, a straight C type interface, to the MCI driver. The syntax for mciSendString is: MCIERROR mciSendString(LPCTSTR lpszCommand, LPTSTR lpszReturnString, UINT cchReturn, HANDLE hwndCallback); The pointer lpszCommand points to the MCI command string such as "play from 0 to 100". Consult the Microsoft SDK documentation for more details. The syntax for mciSendCommand is: MCIERROR mciSendCommand(MCIDEVICEID IDDevice, UINT uMsg, DWORD fdwCommand, DWORD dwParam); where uMsg is an MCI command message such as MCI_PLAY defined in an include file. Consult the Microsoft SDK documentation for more details on MCI command messages. mciSendString(...) and mciSendCommand(...) are essentially equivalent. The MCI driver should convert the MCI command string to an MCI command message internally. The MCI command strings provide a more English like interface to MCI. For C++ programmers, Microsoft provides a window class MCIWnd to wrap the MCI operations. Quoting the Microsoft SDK documentation: Microsoft sayeth.... MCIWnd is a window class for controlling multimedia devices. A library of functions, messages, and macros associated with MCIWnd provides a simple method to add multimedia playback or recording capabilities to your applications. Using a single function, your application can create a control that plays devices such as video, CD audio, waveform audio, MIDI (Musical Instrument Digital Interface), or any device that uses the Media Control Interface (MCI). Automating playback is also quick and easy. Using a function and two macros, an application can create an MCIWnd window with the appropriate media device, play the device, and close both the device and the window when the content has finished playing. ... end Microsoft sayeth. Consult the Microsoft documentation for more details on MCIWnd. ActiveMovie appears intended to supersede MCI. ActiveMovie includes a restricted subset of MCI for (partial) backward compatibility. However, Microsoft appears to want developers to switch over to new API's such as ActiveX and ActiveMovie, built on top of Microsoft's Component Object Model (COM) object oriented framework. Return to Top

Reading and Writing an AVI file within a Windows Application

The Microsoft Windows Win32 SDK (Windows NT and Windows 95) includes a set of functions and macros known as AVIFile for reading, writing, and manipulating RIFF files including AVI files within a Windows program. These functions are contained within a Dynamic Link Library avifile.dll. The AVIFile functions include: AVIFileInit(...) AVIFileOpen(...) AVIFileReadData(...) AVIFileWriteData(...) AVIFileExit(...) and many many others. Consult Microsoft documentation for details. Return to Top

Where to get C Source Code for AVI Player Including Many Codecs

Marc Podlipec's Xanim is a free AVI Player for X Windows and Unix. Most of Xanim is available in source code format. The Xanim home page is: Unfortunately, Xanim's Cinepak and Indeo support is only available in object module (binary format). Return to Top

Where to get Detailed Information on Graphics File Formats

Programmers often need to know the details of the many graphics file formats, both still image and moving. There are a number of Web sites, books, and other resources that provide detailed information on the many still image and video/animation graphics file formats. Wotsit's File Format Collection and Return to Top

Where to get Detailed Information on Audio File Formats

On the Internet, Guido Van Rossum distributes an Audio Formats FAQ (in two parts) to the alt.binaries.sounds.misc, alt.binaries.sounds.d, and comp.dsp USENET newsgroups. On the Web: Return to Top

Where to get C Source Code for a JPEG Encoder or Decoder?

Maybe you want to write your own Motion JPEG codec for AVI. It happens. The Independent JPEG Group, also known as IJG, distributes the source code for a JPEG encoder and decoder. The IJG code is incorporated in many JPEG viewers, is optimized, is free. This is available by anonymous ftp from the UUNET FTP archive. Return to Top

Where to get C Source Code for an H.263 Video Encoder or Decoder?

Telenor Research distributed a free H.263 video encoder and decoder. The code is not optimized. Note that H.263 is subject to a variety of patents and Telenor includes a disclaimer with the code. Telenor appears to have ceased distributing the code, although it is still undoubtedly available somewhere on the Web. For a time, the Signal Processing and Multimedia Group at the University of British Columbia distributed a free H.263+ video encoder and decoder. They also appear to have ceased distribution. Their code appears to be available for a licensing fee. See also, their article (available in Adobe PDF format at their web site): "H.263+: Video Coding at Low Bit Rates", Guy Cote, Berna Erol, Michael Gallant, and Faouzi Kossentini, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 8, No. 7, November 1998, p. 849-866 Return to Top

Where to get C Source Code for an MPEG Video Encoder or Decoder?

The MPEG Software Simulation Group or MSSG distributes the C source code for MPEG-1 and MPEG-2 video encoders and decoders. This code is not optimized. Go to the MPEG site below and look for MSSG. Return to Top

Where to get C/C++ Source Code for Wavelet Image Compression?

Geoff Davis distributes a C/C++ source code for wavelet still image compression of grayscale images, the Wavelet Image Construction Kit. This code is made available for research purposes. Also see the SPIHT demonstration programs, Return to Top

Where to get an Explanation of Color, Color Spaces, Gamma, and All That

Charles Poynton maintains an FAQ on Color and an FAQ on Gamma. This is posted in USENET newsgroups regularly and is available on the Web. Return to Top

Setup Information or INF Files

When a video codec or hardware device driver is installed under Windows 3.x, Windows 95, or Windows NT, Windows uses a special file known as a Setup Information file. This is also known as a Device Information file in the case of device drivers. These files have the extension .INF and are also known as INF files. When a user installs a codec or device driver through the Control Panel, the user points the Windows system to a directory containing an INF file and the various files, such as VxD's or DLLs, to be installed. A Setup Information, Device Information, or INF file contains directives that tell Windows how to install the new software or hardware. These include changes to the Windows Registry, names and locations of files to install, and other things. If you are providing a hardware or software product, you may need to create an INF file to install your product, driver, etc. End users are often unaware of the INF file. Indeed, its purpose is to hide the complexity of installing hardware or software. But it is good to be aware that these files exist and Windows needs them to properly install many drivers, codecs, and so forth. Where AVI is concerned, there are frequently INF files for video codecs, video display adapters, and video capture cards. Return to Top

© 2000 by John F. McGowan, Ph.D.