AVISTREAMINFO

Article
12/10/2007

The AVISTREAMINFO structure contains information for a single stream.

typedef struct { 
    DWORD fccType; 
    DWORD fccHandler; 
    DWORD dwFlags; 
    DWORD dwCaps; 
    WORD  wPriority; 
    WORD  wLanguage; 
    DWORD dwScale; 
    DWORD dwRate; 
    DWORD dwStart; 
    DWORD dwLength; 
    DWORD dwInitialFrames; 
    DWORD dwSuggestedBufferSize; 
    DWORD dwQuality; 
    DWORD dwSampleSize; 
    RECT  rcFrame; 
    DWORD dwEditCount; 
    DWORD dwFormatChangeCount; 
    TCHAR szName[64]; 
} AVISTREAMINFO;

Members

fccType

Four-character code indicating the stream type. The following constants have been defined for the data commonly found in AVI streams:

Constant	Description
streamtypeAUDIO	Indicates an audio stream.
streamtypeMIDI	Indicates a MIDI stream.
streamtypeTEXT	Indicates a text stream.
streamtypeVIDEO	Indicates a video stream.

fccHandler

Four-character code of the compressor handler that will compress this video stream when it is saved (for example, mmioFOURCC('M','S','V','C')). This member is not used for audio streams.

dwFlags

Applicable flags for the stream. The bits in the high-order word of these flags are specific to the type of data contained in the stream. The following flags are defined:

AVISTREAMINFO_DISABLED

Indicates this stream should be rendered when explicitly enabled by the user.

AVISTREAMINFO_FORMATCHANGES

Indicates this video stream contains palette changes. This flag warns the playback software that it will need to animate the palette.

dwCaps

Capability flags; currently unused.

wPriority

Priority of the stream.

wLanguage

Language of the stream.

dwScale

Time scale applicable for the stream. Dividing dwRate by dwScale gives the playback rate in number of samples per second.

For video streams, this rate should be the frame rate. For audio streams, this rate should correspond to the audio block size (the nBlockAlign member of the WAVEFORMAT or PCMWAVEFORMAT structure), which for PCM (Pulse Code Modulation) audio reduces to the sample rate.

dwRate

Rate in an integer format. To obtain the rate in samples per second, divide this value by the value in dwScale.

dwStart

Sample number of the first frame of the AVI file. The units are defined by dwRate and dwScale. Normally, this is zero, but it can specify a delay time for a stream that does not start concurrently with the file.

The 1.0 release of the AVI tools does not support a nonzero starting time.

dwLength

Length of this stream. The units are defined by dwRate and dwScale.

dwInitialFrames

Audio skew. This member specifies how much to skew the audio data ahead of the video frames in interleaved files. Typically, this is about 0.75 seconds.

dwSuggestedBufferSize

Recommended buffer size, in bytes, for the stream. Typically, this member contains a value corresponding to the largest chunk in the stream. Using the correct buffer size makes playback more efficient. Use zero if you do not know the correct buffer size.

dwQuality

Quality indicator of the video data in the stream. Quality is represented as a number between 0 and 10,000. For compressed data, this typically represents the value of the quality parameter passed to the compression software. If set to - 1, drivers use the default quality value.

dwSampleSize

Size, in bytes, of a single data sample. If the value of this member is zero, the samples can vary in size and each data sample (such as a video frame) must be in a separate chunk. A nonzero value indicates that multiple samples of data can be grouped into a single chunk within the file.

For video streams, this number is typically zero, although it can be nonzero if all video frames are the same size. For audio streams, this number should be the same as the nBlockAlign member of the WAVEFORMAT or WAVEFORMATEX structure describing the audio.

rcFrame

Dimensions of the video destination rectangle. The values represent the coordinates of upper left corner, the height, and the width of the rectangle.

dwEditCount

Number of times the stream has been edited. The stream handler maintains this count.

dwFormatChangeCount

Number of times the stream format has changed. The stream handler maintains this count.

szName

Null-terminated string containing a description of the stream.

Requirements

**  Windows NT/2000/XP:** Included in Windows NT 3.1 and later.
**  Windows 95/98/Me:** Included in Windows 95 and later.
**  Header:** Declared in Vfw.h.
**  Unicode:** Declared as Unicode and ANSI structures.

AVISTREAMINFO

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