KB155360 - How To Use MCI to Play AVI/WAVE Files from Memory

SUMMARY

MCI (Media Control Interface) provides a high-level interface to play multimedia files (or "device elements" as defined in MCI). By default, MCI WAVE/AVI drivers (MCIAVI and MCIWAVE) use mmioOpen to open a file. If the file name contains a "+" character, mmioOpen will look for a custom procedure as identified by the three-character file extension to handle the reading and writing of a file. This technique can be applied to allow MCI to play WAVE/AVI files that are already loaded into memory.

The following steps demonstrate this approach. We use "MEY" as the file extension in this example:

Install a custom MMIO procedure as follows:

      mmioInstallIOProc(mmioFOURCC('M', 'E', 'Y', ' '), (LPMMIOPROC)IOProc,
            MMIO_INSTALLPROC | MMIO_GLOBALPROC);

Note that IOProc is the name of the custom procedure.

Use the MCI open command except to add a plus sign (+) at the end of a file name. For instance,
open test.MEY+ type waveaudio (or avivideo) alias test
Because there is a "+" character in the file name, mmioOpen will not open any files. Instead, the custom mmio procedure is identified. Subsequently, all the I/O messages are routed to that procedure.
Then, we can use usual MCI command. For instance:
play test
close test

When done with this custom mmio procedure, we should remove it by

      mmioInstallIOProc(mmioFOURCC('M', 'E', 'Y', ' '), NULL,
      MMIO_REMOVEPROC);

MORE INFORMATION

static char * lpData; static long fileSize; LRESULT CALLBACK IOProc(LPMMIOINFO lpMMIOInfo, UINT uMessage, LPARAM lParam1, LPARAM lParam2) { static BOOL alreadyOpened = FALSE; switch (uMessage) { case MMIOM_OPEN: if (alreadyOpened) return 0; alreadyOpened = TRUE; lpMMIOInfo->lDiskOffset = 0; return 0; case MMIOM_CLOSE: return 0; case MMIOM_READ: memcpy((void *)lParam1, lpData+lpMMIOInfo->lDiskOffset, lParam2); lpMMIOInfo->lDiskOffset += lParam2; return (lParam2); case MMIOM_SEEK: switch (lParam2) { case SEEK_SET: lpMMIOInfo->lDiskOffset = lParam1; break; case SEEK_CUR: lpMMIOInfo->lDiskOffset += lParam1; case SEEK_END: lpMMIOInfo->lDiskOffset = fileSize - 1 - lParam1; break; } return lpMMIOInfo->lDiskOffset; default: return -1; // Unexpected msgs. For instance, we do not // process MMIOM_WRITE in this sample }// end of switch }//end of IOProc