All Databases Inside Mac - Sound Mgr

Playing Sampled Sounds From Files

Playing Sampled Sounds From Files Controlling continuous playback

There are three functions that you can use to initiate and control a continuous

playback of sampled sounds stored in files-SndStartFilePlay,

SndPauseFilePlay, and SndStopFilePlay. You use SndStartFilePlay to

initiate the playing of the sound. You use SndPauseFilePlay to temporarily

suspend a sound from playing. If a sound is playing and you call

SndPauseFilePlay, then the sound is paused. If the sound is paused and you

call SndPauseFilePlay again, then the sound resumes playing. Hence, the

SndPauseFilePlay routine acts like a pause button on a tape player, which

toggles the tape between playing and pa using. (You can determine the current

state of a play from disk by using the SndChannelStatus function. See

complete details ,Obtaining Information About a Single Sound

Channel under the section,

Obtaining Information About Sound Features.) Finally, you can use

SndStopFilePlay to stop the file from playing.

SndStartFilePlay can play sampled sounds stored in 'snd ' resources

(either format 1 or format 2) or in files that conform to the AIFF or

AIFF-C format. In addition, you can specify whether the play from disk should

be asynchronous or synchronous. The SndStartFilePlay function is a

high-level Sound Manager routine, like SndPlay. If you specify NULL as

the sound channel, then SndStartFilePlay allocates memory for a channel

internally. However, since you must specify a sound-channel pointer when

calling either SndPauseFilePlay or SndStopFilePlay, you must allocate a

sound channel yourself and call SndStartFilePlay

asynchronously if you want to be able to pause or stop the sound prior to its

natural ending point.

Playing an 'snd ' Resource From Disk

To play a sampled sound that is contained in an 'snd ' resource, you need to

pass SndStartFilePlay the resource ID number of the resource to play. The

following code example illustrates how to play an 'snd ' resource

synchronously from disk.

Notice that the second parameter passed to SndStartFilePlay here is set to

0. That parameter is used only when playing files from disk.

// Playing an 'snd ' resource from disk

// Assuming inclusion of MacHeaders

#include

// constants used in routine

#define kTotalSize 16*1024

#define kAsync TRUE // play sound asynchronously

#define kQuietNow TRUE // quiet channel now

// Prototype routine like this prior to calling it

void SyncStartFilePlay( short);

void SyncStartFilePlay (short myResNum)

{

OSErr myErr;

SndChannelPtr mySndChan;

// Prototype for error handling routine

void DoError(OSErr);

// allocate a sound channel

mySndChan = nil;

myErr = SndNewChannel (& mySndChan, sampledSynth, initMono, nil);

if ( myErr )

DoError( myErr);

// play the 'snd ' resource

myErr = SndStartFilePlay( mySndChan, 0, myResNum, kTotalSize, nil,

nil, nil, !kAsync);

// if error occured handle it

if ( myErr )

DoError( myErr);

// dispose of the channel, if soundchannel was allocated

if ( mySndChan )

myErr = SndDisposeChannel( mySndChan, !kQuietNow);

// if error occured, handle it

if ( myErr )

DoError( myErr);

}

Playing a File From Disk

To play a sampled sound that is contained in a file, you need to pass

SndStartFilePlay the file reference number of the file to play. The sample

should be stored in either AIFF or AIFF-C format. If the sample is compressed,

then it will be automatically expanded during playback.

For example, to play a sampled sound that is found in a file whose file

reference number is stored in the variable my fRefNum, you could write

myErr = SndStartFilePlay ( mySndChan, my fRefNum, 0, kTotalSize, NULL, l

NULL,NULL, FALSE);

Notice that the third parameter passed to SndStartFilePlay here is set to 0.

That parameter is used only when playing resources from disk.

Playing Selections

The sixth parameter passed to SndStartFilePlay is a pointer to an

AudioSelection record, which allows you to specify that only part of the

sound be played. If that parameter has a value different from NULL, then

SndStartFilePlay plays only a specified selection of the entire sound. You

indicate which part of the entire sound to play by giving two offsets from the

beginning of the sound, a time at which to start the selection and a time at

which to end the selection. Currently, both time offsets must be specified in

seconds.

Referenced by (2):