AVAssetWriter not recording audio

Question

Im having trouble getting audio recorded into a video using avassetwriter on the iPhone. I am able to record video from the camera on the phone no problem but when I try to add audio I get nothing, also the durations displayed in the video in the photo albums app are showing something really out of whack, a 4 second video will show 15:54:01 or something like that, and every video made after the number increases even if the video is shorter. I've been trying to follow what ive seen in other questions here but no luck.

Heres how I'm setting up my audio inputs

captureSession = [[AVCaptureSession alloc] init];
//set up audio input 
AVCaptureDevice *audioDevice     = [AVCaptureDevice defaultDeviceWithMediaType: AVMediaTypeAudio];
AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error ]; 
audioOutput = [[AVCaptureAudioDataOutput alloc] init];

if([captureSession canAddOutput:audioOutput])
{
    [captureSession addOutput:audioOutput];
}    

[audioOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];

heres how im setting up the AVAssetWriter

videoWriter = [[AVAssetWriter alloc] initWithURL:[NSURL fileURLWithPath:MOVIE_PATH] fileType:AVFileTypeQuickTimeMovie error:&error];

AudioChannelLayout acl;
bzero( &acl, sizeof(acl));
acl.mChannelLayoutTag = kAudioChannelLayoutTag_Mono;


NSDictionary* audioOutputSettings = audioOutputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
         [ NSNumber numberWithInt: kAudioFormatMPEG4AAC], AVFormatIDKey,
         [ NSNumber numberWithInt: 1 ], AVNumberOfChannelsKey,
         [ NSNumber numberWithFloat: 44100.0 ], AVSampleRateKey,
         [ NSData dataWithBytes: &acl length: sizeof( acl ) ], AVChannelLayoutKey,
         [ NSNumber numberWithInt: 64000 ], AVEncoderBitRateKey,
                           nil];

and then here is how im writing the audio sample buffers using the CMSampleBufferRef Sent by the audioOutput call back

- (void) captureAudio:(CMSampleBufferRef)sampleBuffer
 {
   if([audioWriterInput isReadyForMoreMediaData]){
     [audioWriterInput appendSampleBuffer:sampleBuffer];
   }
 }

Would really appreciate any help, I've been stuck on this all day.

Rhythmic Fistman · Answer 1 · 2016-12-06T20:52:02.843

3

I don't see you calling [videoWriter startSessionAtSourceTime], also you're discarding audio sample buffers when audioWriterInput isn't ready (and that can't be what you want).

So your problem lies in the PTSs (Presentation Time Stamps) of what you're writing out. Either you can tell the output that your timeline starts at a given time t with startSessionAtSourceTime or you can modify the buffers you append to have zero based presentationTimeStamps.

edited Dec 06 '16 at 20:52

answered Feb 11 '12 at 19:57

Rhythmic Fistman

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can't find function startSessionAtSourceTime on AVCaptureAudioDataOutput. Did you mean something else? – Werner Kratochwil Dec 05 '16 at 15:45
Yes, this question is about `AVAssetWriter`, a class for encoding audio and video files, and you're asking about `AVCaptureAudioDataOutput` which is for capturing audio from the microphone. You can use `AVAssetWriter` to write the audio you capture with `AVCaptureAudioDataOutput` to a file, and in that case you'd pass the captured buffer's timestamp to `startSessionAtSourceTime`. – Rhythmic Fistman Dec 05 '16 at 21:09
so you did mean to write `[assetWriter startSessionAtSourceTime]` – Werner Kratochwil Dec 06 '16 at 20:28
Oops, I did. I mixed up `AVAssetWriter` and its `AVAssetWriterInput`s. Fixed. – Rhythmic Fistman Dec 06 '16 at 20:53
2

I am calling [videoWriter startSessionAtSourceTime] in my code, and I am still getting no audio. Still searching for answers. anyone else come across this in 2018 (using Swift 4.0) – JCutting8 Aug 02 '18 at 16:55
Did you figure it out? – Shree Ranga Raju Aug 15 '20 at 22:14
Can you start a new question showing some code @ShreeRangaRaju ? – Rhythmic Fistman Aug 15 '20 at 23:10

AVAssetWriter not recording audio

1 Answers1