The chunk granularity is a logical block size for an AVI file that is used for writing and retrieving audio and video data chunks. When writing audio and video chunks to disk, AVICap adds filler chunks (RIFF "JUNK" chunks) as necessary to fill each logical block of data.
You can retrieve the current chunk granularity setting by using the WM_CAP_GET_SEQUENCE_SETUP message (or the capCaptureGetSetup macro). The current chunk granularity is stored in the wChunkGranularity member of the CAPTUREPARMS structure. You can specify a new chunk granularity as the value of wChunkGranularity and then send the updated CAPTUREPARMS structure to the capture window by using the WM_CAP_SET_SEQUENCE_SETUP message (or the capCaptureSetSetup macro). You can also specify zero for this member to set the chunk granularity to the sector size of the disk.