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 //音频会话
AVAudioSession *session = [AVAudioSession sharedInstance];
NSError *sessionError;
/*
AVAudioSessionCategoryPlayAndRecord :录制和播放
AVAudioSessionCategoryAmbient       :用于非以语音为主的应用,随着静音键和屏幕关闭而静音.
AVAudioSessionCategorySoloAmbient   :类似AVAudioSessionCategoryAmbient不同之处在于它会中止其它应用播放声音。
AVAudioSessionCategoryPlayback      :用于以语音为主的应用,不会随着静音键和屏幕关闭而静音.可在后台播放声音
AVAudioSessionCategoryRecord        :用于需要录音的应用,除了来电铃声,闹钟或日历提醒之外的其它系统声音都不会被播放,只提供单纯录音功能.
*/
[session setCategory:AVAudioSessionCategoryPlayAndRecord error:&sessionError];
[session setActive:YES error:nil];
// 录音参数
NSDictionary *setting = [NSDictionary dictionaryWithObjectsAndKeys:
                               [NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,// 编码格式
                               [NSNumber numberWithFloat:8000], AVSampleRateKey, //采样率
                               [NSNumber numberWithInt:2], AVNumberOfChannelsKey, //通道数
                               [NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,  //采样位数(PCM专属)
                               [NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,  //是否允许音频交叉(PCM专属)
                               [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,  //采样信号是否是浮点数(PCM专属)
                               [NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,  //是否是大端存储模式(PCM专属)
                               [NSNumber numberWithInt:AVAudioQualityMax], AVEncoderAudioQualityKey,  //音质
                               nil];
self.audioRecorder.delegate = self;
//开启音频测量
self.audioRecorder.meteringEnabled = YES;
//保存路径
self.audioRecorder = [[AVAudioRecorder alloc] initWithURL:[NSURL URLWithString:filePath] settings:setting error:nil];
//准备 / 开始录音
[self.audioRecorder prepareToRecord];
[self.audioRecorder record];
//暂停录音
[self.audioRecorder pause];
//停止录音
[self.audioRecorder stop];
//删除录音

播放

 AVAudioSession *session = [AVAudioSession sharedInstance];
NSError *sessionError;
[session setCategory:AVAudioSessionCategoryPlayback error:&sessionError];
[session setActive:YES error:nil];
//开启接近监视(靠近耳朵的时候听筒播放,离开的时候扬声器播放)
[[UIDevice currentDevice] setProximityMonitoringEnabled:YES];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(sensorStateChange:)name:UIDeviceProximityStateDidChangeNotification object:nil];
self.audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL URLWithString:filePath] error:nil];
self.audioPlayer.delegate = self;
//准备播放 / 播放
[self.audioPlayer prepareToPlay];
[self.audioPlayer play];
//停止播放
[self.audioPlayer stop];
//暂停播放
[self.audioPlayer pause];
//proximityStateChange:(NSNotificationCenter *)notification方法
if ([[UIDevice currentDevice] proximityState] == YES) {
    //靠近耳朵
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];
} else {
    //离开耳朵
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
}

剪辑，将路径filePath下的音频文件从time截取到time2后在resultPath中输入

 //AVURLAsset是AVAsset的子类,AVAsset类专门用于获取多媒体的相关信息,包括获取多媒体的画面、声音等信息.而AVURLAsset子类的作用则是根据NSURL来初始化AVAsset对象.
AVURLAsset *videoAsset = [AVURLAsset assetWithURL:[NSURL fileURLWithPath:filePath]];
//音频输出会话
//AVAssetExportPresetAppleM4A: This export option will produce an audio-only .m4a file with appropriate iTunes gapless playback data(输出音频,并且是.m4a格式)
AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:videoAsset presetName:AVAssetExportPresetAppleM4A];
//设置输出路径 / 文件类型 / 截取时间段
exportSession.outputURL = [NSURL fileURLWithPath:resultPath];
exportSession.outputFileType = AVFileTypeAppleM4A;
exportSession.timeRange = CMTimeRangeFromTimeToTime(CMTimeMake(time1, 1), CMTimeMake(time2, 1));
[exportSession exportAsynchronouslyWithCompletionHandler:^{
    //exporeSession.status
}];

合成，将路径filePath1和路径filePath2下的音频合成

 //AVURLAsset子类的作用则是根据NSURL来初始化AVAsset对象.
AVURLAsset *videoAsset1 = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:filePath1] options:nil];
AVURLAsset *videoAsset2 = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:filePath2] options:nil];
//音频轨迹(一般视频至少有2个轨道,一个播放声音,一个播放画面.音频有一个)
AVAssetTrack *assetTrack1 = [[videoAsset1 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
AVAssetTrack *assetTrack2 = [[videoAsset2 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
//AVMutableComposition用来合成视频或音频
AVMutableComposition *composition = [AVMutableComposition composition];
AVMutableCompositionTrack *compositionTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
// 把第二段录音添加到第一段后面
[compositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset1.duration) ofTrack:assetTrack1 atTime:kCMTimeZero error:nil];
[compositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset2.duration) ofTrack:assetTrack2 atTime:videoAsset1.duration error:nil];
//输出
AVAssetExportSession *exporeSession = [AVAssetExportSession exportSessionWithAsset:composition presetName:AVAssetExportPresetAppleM4A];
exporeSession.outputFileType = AVFileTypeAppleM4A;
exporeSession.outputURL = [NSURL fileURLWithPath:resultPath];
[exporeSession exportAsynchronouslyWithCompletionHandler:^{
    //exporeSession.status
}];

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