Question

I have to record an audio by mixing multiple audio file. For example, if three audio file are being played, so I have to mix the sound of all those playing audio and record it into a single audio file.
Please help me in this in this, if any working code is there to achieve it.

Thanks in Advance !!

Answer 1

I think I understand what you’re asking.

You want to create a single track using three tracks available to you. Now, you cannot have audio files playing when you try to use them, they’re locked.

You’ll want to use AVMutableComposition, load all the tracks as AVURLAssets and then combine them. Now I’ve only written code to append one file to another file, so my example won’t be complete, but it should point you in the right direction.

// Generate a composition of the two audio assets that will be combined into
// a single track
AVMutableComposition* composition = [AVMutableComposition composition];
AVMutableCompositionTrack* audioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                 preferredTrackID:kCMPersistentTrackID_Invalid];

// grab the two audio assets as AVURLAssets according to the file paths
AVURLAsset* masterAsset = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:self.masterFile] options:nil];
AVURLAsset* activeAsset = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:self.newRecording] options:nil];

NSError* error = nil;

// grab the portion of interest from the master asset
[audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, masterAsset.duration)
                ofTrack:[[masterAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
                 atTime:kCMTimeZero
                  error:&error];
if (error)
{
    // report the error
    return;
}

// append the entirety of the active recording
[audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, activeAsset.duration)
                ofTrack:[[activeAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
                 atTime:masterAsset.duration
                  error:&error];

if (error)
{
    // report the error
    return;
}

// now export the two files
// create the export session
// no need for a retain here, the session will be retained by the
// completion handler since it is referenced there

AVAssetExportSession* exportSession = [AVAssetExportSession
                                   exportSessionWithAsset:composition
                                   presetName:AVAssetExportPresetAppleM4A];
if (nil == exportSession)
{
    // report the error
    return;
}


NSString* combined = @"combined file path";// create a new file for the combined file

// configure export session  output with all our parameters
exportSession.outputURL = [NSURL fileURLWithPath:combined]; // output path
exportSession.outputFileType = AVFileTypeAppleM4A; // output file type

[exportSession exportAsynchronouslyWithCompletionHandler:^{

    // export status changed, check to see if it's done, errored, waiting, etc
    switch (exportSession.status)
    {
        case AVAssetExportSessionStatusFailed:
            break;
        case AVAssetExportSessionStatusCompleted:
            break;
        case AVAssetExportSessionStatusWaiting:
            break;
        default:
            break;
    }
    NSError* error = nil;

    // your code for dealing with the now combined file
}];