iOS Remove Particular Sound from a video

Question

I have an application which plays some audio and also records a video+audio while that sound is playing. I would like to figure out a way to process the video so that the audio that was picked up by the microphone is removed from the resulting video.

For example, if I'm playing audioA, and then recording videoB with audioB (from the microphone), I want to somehow cancel out audioA from the resulting audioB, so that audioB is only the ambient noise and not the noise from the device speakers.

Any idea if there's a way to do this?

Bonus points if it can be done without any offline processing.

Answer 1

You have to deal with Playback part. But here is a code to Mix the selected Audio to the Recorded Video.

- (void)mixAudio:(AVAsset*)audioAsset startTime:(CMTime)startTime withVideo:(NSURL*)inputUrl affineTransform:(CGAffineTransform)affineTransform  toUrl:(NSURL*)outputUrl outputFileType:(NSString*)outputFileType withMaxDuration:(CMTime)maxDuration withCompletionBlock:(void(^)(NSError *))completionBlock {
    NSError * error = nil;
    AVMutableComposition * composition = [[AVMutableComposition alloc] init];

    AVMutableCompositionTrack * videoTrackComposition = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

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

    AVURLAsset * fileAsset = [AVURLAsset URLAssetWithURL:inputUrl options:[NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey]];

    NSArray * videoTracks = [fileAsset tracksWithMediaType:AVMediaTypeVideo];

    CMTime duration = ((AVAssetTrack*)[videoTracks objectAtIndex:0]).timeRange.duration;

    if (CMTIME_COMPARE_INLINE(duration, >, maxDuration)) {
        duration = maxDuration;
    }

    for (AVAssetTrack * track in [audioAsset tracksWithMediaType:AVMediaTypeAudio]) {
        [audioTrackComposition insertTimeRange:CMTimeRangeMake(startTime, duration) ofTrack:track atTime:kCMTimeZero error:&error];

        if (error != nil) {
            completionBlock(error);
            return;
        }
    }

    for (AVAssetTrack * track in videoTracks) {
        [videoTrackComposition insertTimeRange:CMTimeRangeMake(kCMTimeZero, duration) ofTrack:track atTime:kCMTimeZero error:&error];

        if (error != nil) {
            completionBlock(error);
            return;
        }
    }

    videoTrackComposition.preferredTransform = affineTransform;

    AVAssetExportSession * exportSession = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetPassthrough];
    exportSession.outputFileType = outputFileType;
    exportSession.shouldOptimizeForNetworkUse = YES;
    exportSession.outputURL = outputUrl;

    [exportSession exportAsynchronouslyWithCompletionHandler:^ {
        NSError * error = nil;
        if (exportSession.error != nil) {
            NSMutableDictionary * userInfo = [NSMutableDictionary dictionaryWithDictionary:exportSession.error.userInfo];
            NSString * subLocalizedDescription = [userInfo objectForKey:NSLocalizedDescriptionKey];
            [userInfo removeObjectForKey:NSLocalizedDescriptionKey];
            [userInfo setObject:@"Failed to mix audio and video" forKey:NSLocalizedDescriptionKey];
            [userInfo setObject:exportSession.outputFileType forKey:@"OutputFileType"];
            [userInfo setObject:exportSession.outputURL forKey:@"OutputUrl"];
            [userInfo setObject:subLocalizedDescription forKey:@"CauseLocalizedDescription"];

            [userInfo setObject:[AVAssetExportSession allExportPresets] forKey:@"AllExportSessions"];

            error = [NSError errorWithDomain:@"Error" code:500 userInfo:userInfo];
        }

        completionBlock(error);
    }];
}