How to stop AVCaptureSession properly

Question

I'm doing an iOS application that need verification on QR Code with the Hierarchy like this:

View
---Scan View
---Image View - cardBG
---Inside View

When view is loading, the Scan View is hidden.
When user click button to scan, the Inside View and Image View is set hidden, reveal the Scan View.
After the scanning return success, the Inside and Image appear again.

The problem is in step 3: when I stop AVCaptureSession, even in an asynchronous dispatch like in this question, the it takes 8-10 seconds to refresh the view.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    if([_captureSession isRunning])[_captureSession stopRunning];
    AVCaptureInput* input = [_captureSession.inputs objectAtIndex:0];
    [_captureSession removeInput:input];
    AVCaptureVideoDataOutput* output = (AVCaptureVideoDataOutput*)[_captureSession.outputs objectAtIndex:0];
    [_captureSession removeOutput:output];
});

[self.bgImageView setHidden:NO];
[self.insideView setHidden:NO];
[self.scanView setHidden:YES];
[self.previewLayer removeFromSuperlayer];

My question is: How can I get the view to avoid this freeze?

may be you find your answer via this thread http://stackoverflow.com/questions/3741121/how-to-properly-release-an-avcapturesession Thanks. — Banker Mittal, Feb 18 '14 at 06:18

score 2 · Accepted Answer · answered Feb 18 '14 at 05:02

Hard to say without more context. Depends on what is actually causing the delay. Would something like this work?

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    if([_captureSession isRunning])[_captureSession stopRunning];

    dispatch_async(dispatch_get_main_queue(), ^{
      [self.bgImageView setHidden:NO];
      [self.insideView setHidden:NO];
      [self.scanView setHidden:YES];
      [self.previewLayer removeFromSuperlayer];        
    });

    AVCaptureInput* input = [_captureSession.inputs objectAtIndex:0];
    [_captureSession removeInput:input];
    AVCaptureVideoDataOutput* output = (AVCaptureVideoDataOutput*)[_captureSession.outputs objectAtIndex:0];
    [_captureSession removeOutput:output];    

});

score 1 · Answer 2 · answered Feb 18 '14 at 05:13

1

The following code will help you:

if(self.previewLayer) {
    [self.previewLayer removeFromSuperlayer];
    self.previewLayer = nil;
}

if(_captureSession) {
    [_captureSession stopRunning];
    _captureSession = nil;
}

answered Feb 18 '14 at 05:13

Sujith Thankachan

3,508
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Thanks. This helps me too.The reason was I tried to update UI when not in main thread. – anhdat Feb 18 '14 at 07:17

How to stop AVCaptureSession properly

2 Answers2