MMIOM_DECOMPRESS
The MMIOM_DECOMPRESS message is sent to a Multimedia I/O (MMIO) procedure to request that a buffer filled with compressed data be decoded and expanded into raw, uncompressed format.
Syntax
rc = mmioSendMessage(hmmio, MMIOM_DECOMPRESS, (LONG)pMMDecompress, lParam2);
Parameters
- pmmioinfo (PMMIOINFO)
- A pointer to an MMIOINFO data structure maintaining the current state of the open file.
- usMsg (USHORT)
- The message identifier, set to `MMIOM_DECOMPRESS`.
- lParam1 (LONG)
- A pointer to an MMDECOMPRESS structure detailing the compressed source data, target buffer destination, and runtime codec configuration parameters.
- lParam2 (LONG)
- This parameter is not used.
Return Value
- rc (ULONG)
- Return codes indicating success or failure:
- MMIO_SUCCESS: The data in the buffer was decompressed successfully.
- MMIO_ERROR: An error occurred during the decompression sequence, or the compressed payload stream was corrupted.
Remarks
- In-Memory Decoding: Similar to its counterpart MMIOM_COMPRESS, this message handles memory block translations directly. The software or hardware-accelerated codec associated with the file format processes the compressed buffer payload and outputs uncompressed chunks.
- Stream Assembly: Digital video and audio format I/O procedures use this message inside playback loops to expand native frames (such as dynamic audio or packed bitmap frames) into raw wave structures or pixel frames before rendering them to output hardware devices.