iOS:如何在 .aif 录音的开始和结束时修剪静音？

Question

我的应用包含让用户录制简短消息的功能；我想剪掉录音开头和结尾的所有静音(或者更准确地说，剪掉音量低于给定阈值的任何音频)。

我正在使用 AVAudioRecorder 录制音频，并将其保存到 .aif 文件中。我在其他地方看到过一些方法，我可以通过这些方法等到音频电平达到阈值后再开始录制；这会让我走到一半，但无助于结束最后的沉默。

如果有一个简单的方法可以做到这一点，我将永远感激不已!

谢谢。

Answer 1

此项目从麦克风获取音频，在噪音大时触发，在安静时不触发。它还在末端修剪和淡入/淡出。

https://github.com/fulldecent/FDSoundActivatedRecorder

您正在寻找的相关代码:

- (NSString *)recordedFilePath
{
    // Prepare output
    NSString *trimmedAudioFileBaseName = [NSString stringWithFormat:@"recordingConverted%x.caf", arc4random()];
    NSString *trimmedAudioFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:trimmedAudioFileBaseName];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:trimmedAudioFilePath]) {
        NSError *error;
        if ([fileManager removeItemAtPath:trimmedAudioFilePath error:&error] == NO) {
            NSLog(@"removeItemAtPath %@ error:%@", trimmedAudioFilePath, error);
        }
    }
    NSLog(@"Saving to %@", trimmedAudioFilePath);

    AVAsset *avAsset = [AVAsset assetWithURL:self.audioRecorder.url];
    NSArray *tracks = [avAsset tracksWithMediaType:AVMediaTypeAudio];
    AVAssetTrack *track = [tracks objectAtIndex:0];

    AVAssetExportSession *exportSession = [AVAssetExportSession
                                           exportSessionWithAsset:avAsset
                                           presetName:AVAssetExportPresetAppleM4A];

    // create trim time range
    CMTime startTime = CMTimeMake(self.recordingBeginTime*SAVING_SAMPLES_PER_SECOND, SAVING_SAMPLES_PER_SECOND);
    CMTimeRange exportTimeRange = CMTimeRangeFromTimeToTime(startTime, kCMTimePositiveInfinity);

    // create fade in time range
    CMTime startFadeInTime = startTime;
    CMTime endFadeInTime = CMTimeMake(self.recordingBeginTime*SAVING_SAMPLES_PER_SECOND + RISE_TRIGGER_INTERVALS*INTERVAL_SECONDS*SAVING_SAMPLES_PER_SECOND, SAVING_SAMPLES_PER_SECOND);
    CMTimeRange fadeInTimeRange = CMTimeRangeFromTimeToTime(startFadeInTime, endFadeInTime);

    // setup audio mix
    AVMutableAudioMix *exportAudioMix = [AVMutableAudioMix audioMix];
    AVMutableAudioMixInputParameters *exportAudioMixInputParameters =
    [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:track];

    [exportAudioMixInputParameters setVolumeRampFromStartVolume:0.0 toEndVolume:1.0
                                                      timeRange:fadeInTimeRange];
    exportAudioMix.inputParameters = [NSArray
                                      arrayWithObject:exportAudioMixInputParameters];

    // configure export session  output with all our parameters
    exportSession.outputURL = [NSURL fileURLWithPath:trimmedAudioFilePath];
    exportSession.outputFileType = AVFileTypeAppleM4A;
    exportSession.timeRange = exportTimeRange;
    exportSession.audioMix = exportAudioMix;

    // MAKE THE EXPORT SYNCHRONOUS
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    [exportSession exportAsynchronouslyWithCompletionHandler:^{
        dispatch_semaphore_signal(semaphore);
    }];
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

    if (AVAssetExportSessionStatusCompleted == exportSession.status) {
        NSLog(@"AVAssetExportSessionStatusCompleted");
        return trimmedAudioFilePath;
    } else if (AVAssetExportSessionStatusFailed == exportSession.status) {
        // a failure may happen because of an event out of your control
        // for example, an interruption like a phone call comming in
        // make sure and handle this case appropriately
        NSLog(@"AVAssetExportSessionStatusFailed %@", exportSession.error.localizedDescription);
    } else {
        NSLog(@"Export Session Status: %d", exportSession.status);
    }
    return nil;
}