Q: In my program I open an audio file as a QuickTime movie, set the movie's looping state attribute, then start it playing. This all works, and my audio movie properly loops (it automatically starts over again when it finishes), but I experience a very short pause when the movie finishes and starts over. Is there any way to fix this pause?A: This is a known issue in QuickTime (r. 3792717). For short audio loops you may experience this problem. The workaround is to create a temporary movie, and add multiple references to your audio source in this temporary movie (QuickTime allows you to reference the same audio data inside a movie multiple times). Then, when you play the temporary movie you are simply playing references to the same audio file over and over again, which QuickTime can do quite smoothly, without pausing. Adding multiple references (even hundreds) to your source audio file in this manner does not result in a large movie file since each reference contains only a pointer to the actual data, rather than a copy of the data. You will of course hear the pause when the movie finishes, but if your movie contains hundreds of references to the same audio file the pause will only occur once after the audio has repeated hundreds of times. The code snippet below shows how to create a temporary movie with multiple references to the original audio file. Listing 1: Creating a temporary movie with multiple references to an audio file.
// specifies the number of references to the original audio file
// we will add to our temporary movie
#define kRefCount 30
//
// createAudioRefMovie
//
// This code creates a temporary movie
// with multiple references to the
// the specified audio file
//
// Inputs
//
// srcAudioFilePath
// - a full path to any audio file that
// QT understands (an MP3 file for example)
//
// Outputs
//
// - function returns a new movie which
// contains multiple references to the
// audio file specified in the
// srcAudioFilePath parameter
Movie createAudioRefMovie(CFStringRef srcAudioFilePath)
{
Movie tempMovie, srcMovie;
TimeValue srcMovDuration;
OSErr err = noErr;
Handle audioFileDataRef;
OSType audioFileDataRefType;
short i, resID = 0;
assert(srcAudioFilePath != nil);
// create a QuickTime data reference
// for our audio source file
err = QTNewDataReferenceFromFullPathCFString (
srcAudioFilePath,
kQTNativeDefaultPathStyle,
0,
&audioFileDataRef,
&audioFileDataRefType );
assert(err == noErr);
// create a QuickTime movie for the audio file
// using the audio file's data reference
err = NewMovieFromDataRef (
&srcMovie,
newMovieActive,
&resID,
audioFileDataRef,
audioFileDataRefType );
assert(err == noErr);
// initialize our movie
tempMovie = nil;
// create a temporary movie -- we'll add
// references to the audio file to this movie
tempMovie = NewMovie(newMovieActive);
assert(tempMovie != nil);
srcMovDuration = GetMovieDuration(srcMovie);
// add multiple references to our audio file
// Note:
// by not calling BeginMediaEdits/EndMediaEdits
// we are telling QuickTime to *not* copy the
// actual data - this will give us only references
// to the data which are small
for (i = 0; i < kRefCount; ++i)
{
// add a reference to the source audio file to
// our temporary movie
err = InsertMovieSegment (
srcMovie, // our audio file
tempMovie, // temporary movie
0,
srcMovDuration,
GetMovieDuration(tempMovie) );
assert(err == noErr);
}
// for completeness we'll copy the movie settings
// from the source file
err = CopyMovieSettings(srcMovie, tempMovie);
assert(err == noErr);
return tempMovie;
}
Document Revision History| Date | Notes |
|---|
| 2004-09-08 | Demonstrates how to avoid pauses when looping audio files with QuickTime |
Posted: 2004-09-08
|
