在IOS上使用AVComposition混合两个音频文件

Question

我试图混合两个音频文件(将一个音频文件放在另一个音频文件之上，而不是拼接在一起)，但我很难在IOS上学习AVFoundation。我在这里遵循了这个答案：How to merge Audio and video using AVMutableCompositionTrack

这就是我所拥有的

//NSURL *audioFilePath = [NSURL fileURLWithPath:@"var/mobile/Applications/822732B6-67B9-485F-BA44-FAACAB34C4FD/Documents/Coisir Cheoil10_09_2014_1429.m4a"];
NSURL *audioUrl = [NSURL fileURLWithPath:@"var/mobile/Applications/822732B6-67B9-485F-BA44-FAACAB34C4FD/Documents/Robot R-3-311_09_2014_2252.m4a"];
// need to fix link to backing Track
NSURL *backingTrackURL = [NSURL fileURLWithPath:@"var/mobile/Applications/822732B6-67B9-485F-BA44-FAACAB34C4FD/Documents/Robot R-3-316_09_2014_1559.m4a"];// need ot fix the link to this
AVURLAsset* backingTrack = [[AVURLAsset alloc] initWithURL:audioUrl options:nil];
AVURLAsset* voiceTrack = [[AVURLAsset alloc] initWithURL:backingTrackURL options:nil];

AVMutableComposition* mixComposition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionCommentaryTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];


[compositionCommentaryTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, backingTrack.duration)
                                    ofTrack:[[backingTrack tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0]
                                     atTime:kCMTimeZero
                                      error:nil];

AVMutableCompositionTrack *compositionVoiceTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

[compositionVoiceTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, voiceTrack.duration)
                               ofTrack:[[voiceTrack tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0] atTime:kCMTimeZero error:nil];

AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];

NSString* mixedAudio = @"mixedAudio.m4a";

NSString *exportPath = [NSTemporaryDirectory() stringByAppendingString:mixedAudio];
NSURL *exportURL = [NSURL fileURLWithPath:exportPath];

if ([[NSFileManager defaultManager]fileExistsAtPath:exportPath]) {
    [[NSFileManager defaultManager]removeItemAtPath:exportPath error:nil];
}
_assetExport.outputFileType = @"m4a";
_assetExport.outputURL = exportURL;
_assetExport.shouldOptimizeForNetworkUse = YES;

[_assetExport exportAsynchronouslyWithCompletionHandler:^{
    NSLog(@"Completed Sucessfully");
}];

The code fails when I try to set the timeranges with an error index 0 beyond bounds for empty array.  I take it that backing track does not include tracksWithMediaTye:AvMediaTypeAudio and that is why that fails.  

我怀疑这是因为我加载的是.m4a音频文件，而不是像StackOverflow最初的答案那样的视频文件。因此，我的问题是如何混合两个独立的音频文件，并将它们保存为一个新的组合文件。使用的是我有一个回音轨道，用户记录他们自己的声音，然后可以混合他们的声音与背景音轨，并发送给自己的混合音频。

谢谢你的建议。我发现AVFoundation非常令人生畏。

Answer 1

我正在发布我最终开始工作的代码，以防其他人试图做同样的事情，并想要一些代码示例(我上面的问题是音频文件没有正确加载)。

 [self showActivityIndicator]; // This code takes a while so show the user an activity Indicator
AVMutableComposition *composition = [AVMutableComposition composition];
NSArray* tracks = [NSArray arrayWithObjects:@"backingTrack", @"RobotR33", nil];
NSString* audioFileType = @"wav";

for (NSString* trackName in tracks) {
    AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:trackName ofType:audioFileType]]options:nil];

    AVMutableCompositionTrack* audioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                     preferredTrackID:kCMPersistentTrackID_Invalid];

    NSError* error;
    [audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, audioAsset.duration) ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0] atTime:kCMTimeZero error:&error];
    if (error)
    {
        NSLog(@"%@", [error localizedDescription]);
    }
}
AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetAppleM4A];

NSString* mixedAudio = @"mixedAudio.m4a";

NSString *exportPath = [NSTemporaryDirectory() stringByAppendingString:mixedAudio];
NSURL *exportURL = [NSURL fileURLWithPath:exportPath];

if ([[NSFileManager defaultManager]fileExistsAtPath:exportPath]) {
    [[NSFileManager defaultManager]removeItemAtPath:exportPath error:nil];
}
_assetExport.outputFileType = AVFileTypeAppleM4A;
_assetExport.outputURL = exportURL;
_assetExport.shouldOptimizeForNetworkUse = YES;

[_assetExport exportAsynchronouslyWithCompletionHandler:^{
    [self hideActivityIndicator];
    NSLog(@"Completed Sucessfully");
}];

Answer 2

Swift 3 3

    showActivityIndicator()  
    var composition = AVMutableComposition()
    var tracks: [Any] = ["backingTrack", "RobotR33"]
    var audioFileType: String = "wav"
    for trackName: String in tracks {
        var audioAsset = AVURLAsset(url: URL(fileURLWithPath: Bundle.main.path(forResource: trackName, ofType: audioFileType)), options: nil)
        var audioTrack: AVMutableCompositionTrack? = composition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: kCMPersistentTrackID_Invalid)
        var error: Error?
        try? audioTrack?.insertTimeRange(CMTimeRangeMake(kCMTimeZero, audioAsset.duration), of: audioAsset.tracks(withMediaType: AVMediaTypeAudio)[0], atTime: kCMTimeZero)
        if error != nil {
            print("\(error?.localizedDescription)")
        }
    }
    var _assetExport = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A)
//  Converted with Swiftify v1.0.6355 - https://objectivec2swift.com/
var mixedAudio: String = "mixedAudio.m4a"
var exportPath: String = NSTemporaryDirectory() + (mixedAudio)
var exportURL = URL(fileURLWithPath: exportPath)
if FileManager.default.fileExists(atPath: exportPath) {
    try? FileManager.default.removeItem(atPath: exportPath)
}
assetExport.outputFileType = AVFileTypeAppleM4A
assetExport.outputURL = exportURL
assetExport.shouldOptimizeForNetworkUse = true
assetExport.exportAsynchronously(withCompletionHandler: {() -> Void in
    self.hideActivityIndicator()
    print("Completed Sucessfully")
})