如何在軌道中間啟動AUAudioFilePlayer但循環到開頭？

Question

在iOS中，我正在使用AUAudioFilePlayer ，我試圖在循環整個音軌之前進行10秒的引導。 我將ScheduledAudioFileRegion設置如下，以非零幀開始（詳情請參閱： https ： //developer.apple.com/library/ios/qa/qa1786/_index.html ）

ScheduledAudioFileRegion playRegion;
playRegion.mTimeStamp.mFlags = kAudioTimeStampSampleTimeValid;
playRegion.mTimeStamp.mSampleTime = 0;
playRegion.mCompletionProc = NULL;
playRegion.mCompletionProcUserData = NULL;
playRegion.mAudioFile = audioFileId;
playRegion.mLoopCount = UInt32(-1);
playRegion.mStartFrame = startFrame;
playRegion.mFramesToPlay = UInt32(-1);  // i.e. all of it
_(AudioUnitSetProperty(_audioUnit,
                       kAudioUnitProperty_ScheduledFileRegion,
                       kAudioUnitScope_Global,
                       0,
                       &playRegion,
                       sizeof(playRegion)),
  @"Error setting Audio File Region on the FilePlayer AU");

問題是，當它循環時，它會在startFrame再次啟動。 我是如何從一開始就開始的？

Answer 1

答案是做兩個時間表。 mTimeStamp.mSampleTime是相對於等待播放的預定開始時間的長度：

/////////////////////////////////////////
// PRE-AMBLE
/////////////////////////////////////////

// Tell it to play the whole file with optional looping...
// more details: https://developer.apple.com/library/ios/qa/qa1786/_index.html
ScheduledAudioFileRegion playRegion;
playRegion.mTimeStamp.mFlags = kAudioTimeStampSampleTimeValid;
playRegion.mTimeStamp.mSampleTime = 0;  // PLAY IMMEDIATELY...
playRegion.mCompletionProc = NULL;
playRegion.mCompletionProcUserData = NULL;
playRegion.mAudioFile = audioFileId;
playRegion.mLoopCount = 0;
playRegion.mStartFrame = startFrame;   // ...FROM REQUEST START FRAME
playRegion.mFramesToPlay = UInt32(-1);  // i.e. all of it
_(AudioUnitSetProperty(_audioUnit,
                       kAudioUnitProperty_ScheduledFileRegion,
                       kAudioUnitScope_Global,
                       0,
                       &playRegion,
                       sizeof(playRegion)),
  @"Error setting Audio File Region on the FilePlayer AU");


/////////////////////////////////////////
// LOOP
/////////////////////////////////////////

playRegion.mTimeStamp.mFlags = kAudioTimeStampSampleTimeValid;
playRegion.mTimeStamp.mSampleTime = lengthInFrames - startFrame; // WAIT UNTIL PREAMBLE IS DONE...
playRegion.mCompletionProc = NULL;
playRegion.mCompletionProcUserData = NULL;
playRegion.mAudioFile = audioFileId;
playRegion.mLoopCount = UInt32(-1);
playRegion.mStartFrame = 0;         // ...THEN PLAY FROM THE BEGINNING
playRegion.mFramesToPlay = UInt32(-1);  // i.e. all of it
_(AudioUnitSetProperty(_audioUnit,
                       kAudioUnitProperty_ScheduledFileRegion,
                       kAudioUnitScope_Global,
                       0,
                       &playRegion,
                       sizeof(playRegion)),
  @"Error setting Audio File Region on the FilePlayer AU");