AVCaptureVideoDataOutput

Question

Here's the problem. I am using AVCaptureVideoDataOutput to get video frames from camera and make video from them with AVAssetWriter. Its working OK, but the video that I get is upside down because default orientation of device for my app is landscape left, not landscape right as its stated by default in AVCaptureVideoDataOutput. Im trying to change orientation in AVCaptureConnection class, but isVideoOrientationSupported is always false, is it somehow possible to fix it?

Here is some code:

 AVCaptureDeviceInput *captureInput = [AVCaptureDeviceInput 
            deviceInputWithDevice:[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo] 
            error:nil];
 /*We setupt the output*/
 AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init]; 
 captureOutput.alwaysDiscardsLateVideoFrames = YES; 
 captureOutput.minFrameDuration = CMTimeMake(1.0, 24.0); //Uncomment it to specify a minimum duration for each video frame
 [captureOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];

 // Set the video output to store frame in BGRA (It is supposed to be faster)
 NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey; 
 NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA]; 



 NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key]; 
 [captureOutput setVideoSettings:videoSettings]; 


 /*And we create a capture session*/
 self.captureSession = [[AVCaptureSession alloc] init];
 self.captureSession.sessionPreset = AVCaptureSessionPresetLow;
 /*We add input and output*/
 if ([self.captureSession canAddInput:captureInput]) 
 {
  [self.captureSession addInput:captureInput];
 }
 if ([self.captureSession canAddOutput:captureOutput]) 
 {
  [self.captureSession addOutput:captureOutput];
 }

 /*We add the preview layer*/
 self.prevLayer = [AVCaptureVideoPreviewLayer layerWithSession: self.captureSession];

 if ([self.prevLayer isOrientationSupported]) 
 {
  [self.prevLayer setOrientation:AVCaptureVideoOrientationLandscapeLeft];
 }

 self.prevLayer.frame = self.view.bounds; 

 self.prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
 [self.view.layer addSublayer: self.prevLayer];

 AVCaptureConnection *videoConnection = NULL;

 [self.captureSession beginConfiguration];

 for ( AVCaptureConnection *connection in [captureOutput connections] ) 
 {
  for ( AVCaptureInputPort *port in [connection inputPorts] ) 
  {
   if ( [[port mediaType] isEqual:AVMediaTypeVideo] ) 
   {
    videoConnection = connection;

   }
  }
 }
    if([videoConnection isVideoOrientationSupported]) // **Here it is, its always false**
     {
        [videoConnection setVideoOrientation:AVCaptureVideoOrientationLandscapeLeft];
     }

 [self.captureSession commitConfiguration];

 [self.captureSession startRunning];

Upd: figured that when exporting video, the AVAssetExportSession loses preferredTransform info.

Steve, did you get this working? I wanted to know how you used the AVAssetWriter with this. I want to be able to stream video from the iphone. — nickfox, Oct 1 '10 at 16:37
When you use the URL you get: The "Pastebin" may have expired or been deleted! — GM., Jan 25 '11 at 23:45
@Steve:hi ,now i too having same issue . Did You get any solution ??? how to make AVCaptureConnection with video orientation support???? Plz help me — Asta ni enohpi, Oct 31 '11 at 8:30

Shizam · Accepted Answer · 2011-02-12 17:26:05Z

up vote 5 down vote accepted

I ran into the same problem and poked around the AVCamDemo from WWDC. I don't know why (yet) but if you query your videoConnection right after you create all the inputs/outputs/connections then both isVideoOrientationSupported and supportsVideoOrientation return NO.

However, if you query supportsVideoOrientation or isVideoOrientationSupported at some later point (after the GUI is setup for instance) then it will return YES. For instance I query it right after the user clicks the record button just before I call [[self movieFileOutput] startRecordingToOutputFileURL...]

Give it a try, works for me.

answered Feb 12 '11 at 17:26

Shizam
3,481 2 24 48

Oh wow, this is tricky! But it works. I think Apple should fix this. isVideoOrientationSupported property should be able to be set at the same runloop as AVCaptureOutput is created. Doing it in some later point just unnecessarily makes the code more complicated. Even if there is a reason behind, at least the document should talk about this. I have to manually transform my coordinate to read the pixel before I found this post! – Hlung May 20 '12 at 18:31

Actually, you don't need to do it in a later runloop. You can do this right after you do addOutput: to AVCaptureSession. – Hlung May 20 '12 at 18:41

This is a life saving answer. I really can't understand why nothing about these conditions are mentioned in the documentation. – aqs Sep 8 at 13:59

This is a life saving answer for me – Kashif Dec 19 at 14:07

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score 3 · Answer 2

from here:http://developer.apple.com/library/ios/#qa/qa1744/_index.html#//apple_ref/doc/uid/DTS40011134

Currently, the capture outputs for a movie file (AVCaptureMovieFileOutput) and still image (AVCaptureStillImageOutput) support setting the orientation, but the data output for processing video frames (AVCaptureVideoDataOutput) does not.

AVCaptureVideoDataOutput

How to change video orientation for AVCaptureVideoDataOutput

2 Answers