MainAVIHeader

The MainAVIHeader structure contains global information for the entire AVI file. It is contained within an 'avih' chunk within the LIST 'hdrl' chunk at the beginning of an AVI RIFF file.

typedef sturct {
    ULONG   ulMicroSecPerFrame;
    ULONG   ulMaxBytesPerSec;
    ULONG   ulReserved1;
    ULONG   ulFlags;
    ULONG   ulTotalFrames;
    ULONG   ulInitialFrames;
    ULONG   ulStreams;
    ULONG   ulSuggestedBufferSize;
    ULONG   ulWidth;
    ULONG   ulHeight;
    ULONG   ulReserved {4}
} MainAVIHeader;

The MainAVIHeader structure has the following fields:

Field

Description
ulMicroSecPerFrame
Specifies the number of microseconds between frames.
ulMaxBytesPerSec
Specifies the approximate maximum data rate of file.
ulReserved1
Reserved. (This field should be set to 0.)
ulFlags
Specifies any applicable flags. The following flags are defined:

AVIF_HASINDEX

Indicates the AVI file has an 'idx1' chunk containing an index at the end of the file. For good performance, all AVI files should contain an index.
AVIF_ISINTERLEAVED
Indicates the AVI file is interleaved.
ulTotalFrames
Specifies the number of frames of data in file.
ulInitialFrames
Specifies the initial frame for interleaved files. Non-interleaved files should specify zero.
ulStreams
Specifies the number of streams in the file. For example, a file with audio and video has two (2) streams.
ulSuggestedBufferSize
Specifies the suggested buffer size for reading the file. Generally, this size should be large enough to contain the largest chunk in the file. If set to zero, or if it is too small, the playback software will have to reallocate memory during playback which will reduce performance.

For an interleaved file, this buffer size should be large enough to read an entire record and not just a chunk.

ulWidth
Specifies the width of the AVI file in pixels.
ulHeight
Specifies the height of the AVI file in pixels.
ulReserved
Reserved. These four double words should be set to zero.

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