Reading from a Stream - Win32 Multimedia Programmer's Reference

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Reading from a Stream

You can retrieve information about an open stream by using the AVIStreamInfo function. This function fills the AVISTREAMINFO structure with information such as the type of data in the stream, the compression method used when writing stream data, the suggested buffer size, the playback rate, and a text description of the stream.

Some members of the AVISTREAMINFO structure are also present in the AVIFILEINFO structure. The information in the AVIFILEINFO structure applies to the entire file. The information in the AVISTREAMINFO structure is specific to the accessed stream and has precedence over the information in the AVIFILEINFO structure.

If a stream has supplementary information associated with it, you can retrieve this information by using the AVIStreamReadData function. This function returns the information in an application-supplied buffer. Supplementary stream information might include configuration settings for the compression and decompression methods used on a stream. You can obtain the required buffer size by using the AVIStreamDataSize macro.

You can retrieve formatting information about a stream by using the AVIStreamReadFormat function. This function returns a stream-specific structure in an application-supplied buffer. For a video stream, the buffer contains formatting information in a BITMAPINFO structure. For an audio stream, the buffer contains formatting information in a WAVEFORMATEX or PCMWAVEFORMAT structure. For other stream types, the stream handler returns information specific to the stream. You can determine the required buffer size by using AVIStreamReadFormat and specifying a NULL buffer address or by using the AVIStreamFormatSize macro.

You can retrieve the multimedia content in a stream by using the AVIStreamRead function. This function copies raw data from the stream into an application-supplied buffer. For video streams, this function retrieves the bitmapped images that make up the frame content. For audio streams, this function retrieves waveform-audio samples that make up the sound content. You can determine the required buffer size by using AVIStreamRead and specifying a NULL buffer address or by using the AVIStreamSampleSize macro.

Some AVI stream handlers introduce delays associated with software and hardware initialization or coordination. You can inform these handlers to prepare for data streaming by using the AVIStreamBeginStreaming function. This function lets the stream handler allocate and initialize the resources it needs. To inform these handlers when streaming has ended, use the AVIStreamEndStreaming function. This function lets the stream handler deallocate the resources it allocated for AVIStreamBeginStreaming.

The AVIStreamRead function does not provide decompression services. For information about compressing and decompressing audio streams, see Audio Compression Manager. For information about compressing and decompressing video streams, see Video Compression Manager. For information about compressing and decompressing individual frames in a video stream, see Working with Compressed Video Data in a Stream.

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