AVCaptureSession is not releasing AVCaptureDevice without closing application for usage in DeckLink SDK

Question

When using the AVCaptureSession to connect a AVCaptureDevice the device get's locked by the application and can not be released. The only way the device is truly released is after restarting the app.

We are using AVCaptureSession for previewing the camera and audio level meters. But once we start the actual capture we might need to switch to an alternative capture SDK (in this case DeckLink SDK). How ever the device remains locked by AVFoundation and we can't seem to free it in any way.... It all goes sideways as soon as wel call AVCaptureSession.addInput on the AVCaptureSession from the AVCaptureDevice. And simply iterating the inputs and using AVCaptureSession.removeInput does not seem work.

We setup the session like this:

do {
    try self.selectedVideoDevice.lockForConfiguration()
    try self.selectedAudioDevice?.lockForConfiguration()

    self.cameraSession = AVCaptureSession()

    self.cameraSession?.beginConfiguration()
    self.cameraSession?.sessionPreset = AVCaptureSession.Preset.high

    // Add some outputs... not relevant for the issue at hand?!

    // Add audio input
    if self.selectedAudioDevice != nil {
        let deviceInputAudio = try AVCaptureDeviceInput(device: self.selectedAudioDevice!)
        if self.cameraSession?.canAddInput(deviceInputAudio) ?? false {
            self.cameraSession?.addInput(deviceInputAudio)
        }
    }

    // Add video input
    let deviceInputVideo = try AVCaptureDeviceInput(device: self.selectedVideoDevice)

    if self.cameraSession?.canAddInput(deviceInputVideo) ?? false {
        self.cameraSession?.addInput(deviceInputVideo)
    }

    self.cameraSession?.commitConfiguration()
    self.cameraSession?.startRunning()

    self.selectedVideoDevice.unlockForConfiguration()
    self.selectedAudioDevice?.unlockForConfiguration()

} catch {

}

And try to release using something like this... one of the many tries...

self.cameraSession?.stopRunning()

for output in self.cameraSession?.outputs ?? [] {
    self.cameraSession?.removeOutput(output)
}

for input in self.cameraSession?.inputs ?? [] {
    self.cameraSession?.removeInput(input)
}

self.cameraSession = nil

How ever we can't get the device to be recognized in the DeckLink SDK after using in AVFoundation.

Any ideas would be great as cleaning up or setting the variables to nil doesn't seem to do anything...

Answer 1

We chose to implement the Desktop Video SDK from Blackmagic and do all captures from a Blackmagic device using that. This solves more issues when capturing using Blackmagic Mini Recorder (for example: audio sync) somehow AVFoundation does work with Blackmagic but not really well. And Blackmagic officially never answered the question "Do you support AVFoundation". So in order to make it work I would recommend the Desktop Video SDK that can be downloaded from their site under Support.

https://www.blackmagicdesign.com/support/

Also make sure you never load the video device into your AVFoundation workflow. It will get stuck and hold it. So first check if it's Blackmagic then continue to AVFoundation if not.