Composing Video and Audio - Video's Audio Is Gone

Composing Video and Audio - Video's audio is gone

You can adjust volume for video and audio separately @Faruk, Here a is little bit code for that.

        //Extract audio from the video and the music
let audioMix: AVMutableAudioMix = AVMutableAudioMix()
var audioMixParam: [AVMutableAudioMixInputParameters] = []

let assetVideoTrack: AVAssetTrack = assetVideo.tracksWithMediaType(AVMediaTypeAudio)[0]
let assetMusicTrack: AVAssetTrack = assetMusic.tracksWithMediaType(AVMediaTypeAudio)[0]

let videoParam: AVMutableAudioMixInputParameters = AVMutableAudioMixInputParameters(track: assetVideoTrack)
videoParam.trackID = compositionAudioVideo.trackID

let musicParam: AVMutableAudioMixInputParameters = AVMutableAudioMixInputParameters(track: assetMusicTrack)
musicParam.trackID = compositionAudioMusic.trackID

//Set final volume of the audio record and the music
videoParam.setVolume(volumeVideo, atTime: kCMTimeZero)
musicParam.setVolume(volumeAudio, atTime: kCMTimeZero)

//Add setting
audioMixParam.append(musicParam)
audioMixParam.append(videoParam)

//Add audio on final record
//First: the audio of the record and Second: the music
do {
try compositionAudioVideo.insertTimeRange(CMTimeRangeMake(kCMTimeZero, assetVideo.duration), ofTrack: assetVideoTrack, atTime: kCMTimeZero)
} catch _ {
assertionFailure()
}

do {
try compositionAudioMusic.insertTimeRange(CMTimeRangeMake(CMTimeMake(Int64(startAudioTime * 10000), 10000), assetVideo.duration), ofTrack: assetMusicTrack, atTime: kCMTimeZero)
} catch _ {
assertionFailure()
}

//Add parameter
audioMix.inputParameters = audioMixParam

let completeMovie = "\(docsDir)/\(randomString(5)).mp4"
let completeMovieUrl = NSURL(fileURLWithPath: completeMovie)
let exporter: AVAssetExportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality)!

exporter.outputURL = completeMovieUrl
exporter.outputFileType = AVFileTypeMPEG4
exporter.audioMix = audioMix
exporter.exportAsynchronouslyWithCompletionHandler({ 

switch exporter.status {

case AVAssetExportSessionStatus.Completed:
    print("success with output url \(completeMovieUrl)")
    case  AVAssetExportSessionStatus.Failed:
        print("failed \(String(exporter.error))")
    case AVAssetExportSessionStatus.Cancelled:
        print("cancelled \(String(exporter.error))")
    default:
        print("complete")
    }            
})

}

Composing video and audio using AVMutableComposition

The problem lays in:

videoCompositionTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

audioCompositionTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

They need to be moved outside the for loop body.

No audio when writing video using write_videofile

Specifying the codec of audio (audio_codec="aac") while writing the video using write_videofile fixed the issue.

Merge two videos with audio and video together in iOS

The problem is that you are adding a second video track to the composition. You need to insert both videos into the same video track. Just delete your let videoTrack2 and go from there.

AVFoundation no audio tracks for long videos

My guess is that AVCaptureMovieFileOutput has better support for QuickTime containers (.qt, .mov) than for mp4 although it is the industry standard. For instance when writing a movie file in fragments to an .mp4, something probably happens to the fragment table (sample table).

So you could either change the file format to .mov or turn of writing the file in fragments. See this question:
ios-8-ipad-avcapturemoviefileoutput-drops-loses-never-gets-audio-track-after

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