In addition to specifying files or Resource Interchange File Format (RIFF) chunks to be loaded by compound devices, you also can specify memory objects. You create memory objects, for example, to play synthesized audio using the waveform audio media driver. These memory objects can be placed under the control of the memory playlist.
The memory playlist is a data structure in an application. It contains an array of simple, machine-like instructions you formulate, each of which has a fixed format consisting of a 32-bit operation code and three 32-bit operands. Playlist instructions are described in the following table.
To have playlist instructions interpreted by the playlist processor, you specify the MCI_OPEN_PLAYLIST flag with the MCI_OPEN command message. This flag indicates that the pszElementName field in the MCI_OPEN_PARMS data structure is a pointer to a memory playlist.
Using playlist instructions, you can play audio objects in succession from one or more memory buffers. Instructions include branching to and returning from subroutines within the playlist. In addition, the playlist can be modified dynamically by the application while it is being played. Because less overhead is involved when playing audio data from memory, playlist programs will have higher performance. If your application requires speed or if it needs to modify the data before it is sent to the audio device, use playlists.
旼컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿎ommand 쿏escription � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿍RANCH_OPERATION 쿟ransfers control to another instruction in the � � 쿾laylist. � � 쿚perand 1-Ignored. � � 쿚perand 2-The absolute instruction number in the � � 쿾laylist to which control is being transferred. � � 쿍ecause the playlist is defined as an array of � � 퀂tructures (instruction, operation, and operand � � 퀆alues) its first instruction is referenced as � � 쿪rray element, index 0. Therefore, the first � � 쿶nstruction in the list is 0, the second � � 쿶nstruction is 1, and so on. � � 쿚perand 3-Ignored. � � 쿍ranching out of a subroutine is not prohibited; � � 쿴owever, it is not recommended because an unused � � 퀁eturn address is left on the stack maintained by � � 퀃he playlist processor. � � 쿌n application can enable or disable a � � 쿍RANCH_OPERATION by exchanging it with a � � 쿙OP_OPERATION. Operands for a NOP_OPERATION are � � 쿶gnored. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿎ALL_OPERATION 쿟ransfers control to the absolute instruction � � 쿻umber specified in Operand 2, saving the number � � 쿽f the instruction following the CALL for use on a� � 쿝ETURN instruction. � � 쿎ALL instructions may be nested up to 20 levels. � � 쿚perand 1-Ignored. � � 쿚perand 2-Absolute instruction number in the � � 쿾laylist to which control is being transferred. � � 쿚perand 3-Ignored. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿎UEPOINT_OPERATION 쿎auses a cue point data record to be entered into � � 퀃he data stream. Note that the cue point is � � 퀁elative to the DATA_OPERATION that follows it. � � 쿚perand 1-User-defined parameter to be returned as� � 퀃he low word of ulMsgParam1 in the MM_MCICUEPOINT � � 쿺essage. � � 쿚perand 2-Offset in MMTIME units for the actual � � 퀃ime the CUEPOINT message should be generated. � � 쿚perand 3-Ignored. � � 쿟he MM_MCICUEPOINT message is returned to the � � 쿪pplication as soon as possible after the cue � � 쿾oint data record is encountered in the data � � 퀂tream. The message is sent to the window handle � � 퀂pecified when the device was originally opened. � � 쿙ote: The CUEPOINT instruction is ignored when � � 퀅sed in a recording operation. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿏ATA_OPERATION 쿞pecifies a data buffer to be played from or � � 퀁ecorded into. � � 쿚perand 1-Long pointer to a buffer in the � � 쿪pplication. � � 쿚perand 2-Length of the buffer pointed to by � � 쿚perand 1. � � 쿚perand 3-Current position in the buffer. This � � 쿽perand is updated by the system during a � � 퀁ecording or playback operation. For a playback � � 쿽peration, it is the number of bytes that have � � 쿫een sent to the output device handler. For a � � 퀁ecording operation, it is the number of bytes � � 퀃hat have been placed into a user buffer. � � 쿟he current position in the buffer is particularly� � 쿶mportant after a recording operation, because � � 퀃his field contains the number of bytes of � � 퀁ecorded data. The remaining bytes in the buffer � � 쿪re not valid. This field is initialized to zero � � 퀇hen the DATA_OPERATION statement is first � � 쿮ncountered. � � 쿟he buffer indicated by the DATA instruction must � � 쿽nly contain the raw data bytes from the device � � 쿪nd cannot include any header information. � � 쿟herefore, the precise meaning or format of the � � 쿭ata is dependent on the current settings of the � � 쿺edia device. For example, a wave audio data � � 쿮lement is assumed to have the format PCM or � � 쿌DPCM, number of bits per sample, and so on, that � � 쿶s indicated by the settings of the audio device. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿐XIT_OPERATION 쿔ndicates the end of the playlist. � � 쿚perand 1-Ignored. � � 쿚perand 2-Ignored. � � 쿚perand 3-Ignored. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿗OOP_OPERATION 쿎ontrols iteration in a playlist. It is the � � 퀁esponsibility of the application to initialize � � 퀃he current iteration. The current iteration is � � 퀁eset to zero following loop termination. � � 쿚perand 1-Number of times the loop is to be � � 쿮xecuted. � � 쿚perand 2-Target instruction to branch to, when � � 퀃he loop condition fails. � � 쿚perand 3-Current iteration. � � 쿟he last instruction in a loop is a branch back to� � 퀃he LOOP_OPERATION. The operation of the � � 쿗OOP_OPERATION instruction is as follows: � � �1. If Operand 3 is less than Operand 1, control is� � 퀃ransferred to the playlist instruction following � � 퀃he LOOP instruction, and the iteration count in � � 쿚perand 3 is incremented. � � �2. Otherwise, the iteration count is reset to zero� � 쿪nd control is passed to the instruction specified� � 쿶n Operand 2. � � 쿟ypically, the application sets the iteration � � 쿬ount to zero when the playlist is passed to the � � 쿭evice, but this is not required. The loop � � 쿶nstruction merely compares the loop count with � � 퀃he iteration count. If the iteration count is set� � 퀃o a value other than zero when the playlist is � � 쿾assed in, it is as if the loop has been executed � � 퀃hat number of times. Also, if a playback � � 쿽peration is stopped, and then the same playlist � � 쿶s loaded again, the loop iteration count is not � � 쿶nitialized by the playlist processor. � � 쿔t is the application's responsibility to see that� � 쿶teration count values are what is required when � � 퀂witching from play to record, record to play, and� � 퀇hen changing settings for the data (for example, � � �bitspersample, samplespersec, and so on) with the � � 퀂et command. These commands cause the playlist � � 퀂tream to be destroyed and re-created, and the � � 쿾laylist to be reassociated as a new playlist with� � 퀃he playlist processor. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿘ESSAGE_OPERATION 쿝eturns a message to the application during � � 쿾laylist processing. � � 쿚perand 1-Ignored. � � 쿚perand 2-ULONG that is returned to the � � 쿪pplication in the MM_MCIPLAYLISTMESSAGE message � � 쿘sgParam2. � � 쿚perand 3-Ignored. � � 쿐ach time the playlist processor encounters a � � 쿘ESSAGE instruction, MM_MCIPLAYLISTMESSAGE is � � 퀁eturned to the application. MESSAGE instructions � � 쿬an be used by the application to trace specific � � 쿾oints during the execution of the playlist � � 쿾rocessor. The message is sent to the window � � 쿴andle specified when the device was originally � � 쿽pened. � � 쿟his function is not intended to be used for � � 퀃iming of data production or consumption � � 쿶dentified by previously interpreted instructions.� � 쿏o not rely on the MESSAGE instruction to indicate� � 쿾recisely when a particular piece of digital audio� � 쿴as been played by an audio device; however, the � � 쿘ESSAGE instruction can be used to indicate when a� � 쿫uffer has been consumed and needs to be refilled.� 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿙OP_OPERATION 쿢sed as a placeholder. � � 쿚perand 1-Ignored. � � 쿚perand 2-Ignored. � � 쿚perand 3-Ignored. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿝ETURN_OPERATION 쿟ransfers control to the playlist instruction � � 쿯ollowing the most recently executed CALL � � 쿶nstruction. � � 쿚perand 1-Ignored. � � 쿚perand 2-Ignored. � � 쿚perand 3-Ignored. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿞EMPOST_OPERATION 쿎auses the playlist processor to post an event � � 퀂emaphore. The playlist processor will call � � 쿏osWaitEventSem. � � 쿚perand 1-Contains the semaphore to post. � � 쿚perand 2-Ignored. � � 쿚perand 3-Ignored. � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 쿞EMWAIT_OPERATION 쿎auses the playlist processor to wait on a � � 퀂emaphore. The playlist processor will call � � 쿏osWaitEventSem. � � 쿚perand 1-Contains the semaphore to perform the � � 퀇ait on. � � 쿚perand 2-Amount of time the semaphore should � � 퀇ait. � � 쿚perand 3-Boolean value indicating whether or not � � 퀃he semaphore should be cleared before waiting. � 읕컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�