File and stream handlers are drivers that provide consistent interfaces to an application that controls multimedia data. The file and stream handlers included in the operating system use video and waveform-audio data stored in audio-video interleaved (AVI) and waveform-audio files.
You can write handlers to allow your application to write or access multimedia data from another source, such as a file using a proprietary format, an AVI file that has been expanded to contain additional data streams, or a handler that generates its own multimedia data. If you have a custom file format for AVI data that you would like to use with the AVIFile functions and macros, you need to write a custom handler.