The ICM_DECOMPRESSEX_BEGIN message is sent to a video compression driver for decompressing data. When the driver receives this message, it should allocate buffers and do any time-consuming operations so that it can process ICM_DECOMPRESSEX messages efficiently.
Returns ICERR_OK if the specified decompression is supported. Otherwise returns ICERR_BADFORMAT, indicating that the input or output format is not supported.
To have the driver decompress data directly to the screen, an application sends the ICM_DRAW_BEGIN message.
The ICM_DECOMPRESSEX_BEGIN and ICM_DECOMPRESSEX_END messages do not nest. If your driver receives an ICM_DECOMPRESSEX_BEGIN message before decompression is stopped with ICM_DECOMPRESSEX_END, it should restart decompression with new parameters.