MMProgRef - CODEC Messages

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Multimedia Programming Reference

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CODEC procedure messages can be sent to a CODEC procedure as a result of an MMIO function call. For example, the MMIOM_CODEC_OPEN message is sent to a CODEC procedure when mmioOpen is called.

CODEC procedures can also be loaded and called directly, without using mmioSendMessage. The mmioLoadCODECProc function loads a CODEC procedure and returns the entry point. A call to this entry point with an MMIOM_CODEC_OPEN message returns an HCODEC, which is used to identify the open instance on all other calls to the CODEC.

The following syntax is required for a direct CODEC procedure call:

typedef LONG (APIENTRY CODECPROC) (PHCODEC phcodec,
                                   USHORT usMsg,
                                   LONG lParam1,
                                   LONG lParam2);
typedef CODECPROC *PCODECPROC;

Note that OS/2 multimedia currently supports image and video CODECs. OS/2 multimedia does provide a set of audio CODECs, but does not provide a public interface to install new audio CODECs or to interface to audio CODECs directly.

All CODEC procedures must support the following messages. However, if a CODEC is a compressor only, MMIOM_CODEC_DECOMPRESS does not need to be supported. The same is true if a CODEC is a decompressor only; MMIOM_CODEC_COMPRESS does not need to be supported.

Message	Description
MMIOM_CODEC_CLOSE	Requests close of instance specified by phCODEC.
MMIOM_CODEC_COMPRESS	Requests CODEC to compress the data.
MMIOM_CODEC_DECOMPRESS	Requests CODEC to decompress the data.
MMIOM_CODEC_OPEN	Requests CODEC to open an instance.
MMIOM_CODEC_QUERYNAME	Requests the name of the CODEC.
MMIOM_CODEC_QUERYNAMELENGTH	Requests the length of the CODEC name.