iOS AVCaptureSession - How to get/set the number o

问题:

I'm new to AVCaptureSession and wish to better understand how to work with it. So I managed capturing the video stream as separated CIImages and convert them to UIImages. Now I wish to be able to get the number of Frames Per Second captured and preferably to be able to set it.

Any idea how to do that?

回答1:

You could use AVCaptureConnection's videoMinFrameDuration accessor to set the value.

See the AVCaptureConnection documentation

Consider output be AVCaptureVideoDataOutput object.

AVCaptureConnection *conn = [output connectionWithMediaType:AVMediaTypeVideo];

if (conn.isVideoMinFrameDurationSupported)
    conn.videoMinFrameDuration = CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND);
if (conn.isVideoMaxFrameDurationSupported)
    conn.videoMaxFrameDuration = CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND);

More info, see my answer in this SO question

回答2:

AVCaptureConnection's videoMinFrameDuration is deprecated.

You can use AVCaptureDevice properties to detect supported video frame rate ranges and can assign minimum and maximum frame rates using properties.

device.activeFormat.videoSupportedFrameRateRanges return all video frame rates ranges supported by device.

device.activeVideoMinFrameDuration and device.activeVideoMaxFrameDuration can be used for specifying frame durations.

回答3:

To set the capture session frame rate, you have to set it on the device using device.activeVideoMinFrameDuration and device.activeVideoMaxFrameDuration (if necessary).

In Swift 4 you can do something like this:

extension AVCaptureDevice {
    func set(frameRate: Double) {
    guard let range = activeFormat.videoSupportedFrameRateRanges.first,
        range.minFrameRate...range.maxFrameRate ~= frameRate
        else {
            print("Requested FPS is not supported by the device's activeFormat !")
            return
    }

    do { try lockForConfiguration()
        activeVideoMinFrameDuration = CMTimeMake(value: 1, timescale: Int32(frameRate))
        activeVideoMaxFrameDuration = CMTimeMake(value: 1, timescale: Int32(frameRate))
        unlockForConfiguration()
    } catch {
        print("LockForConfiguration failed with error: \(error.localizedDescription)")
    }
  }
}

And call it

device.set(frameRate: 60)

回答4:

Do it like this

if let frameSupportRange = currentCamera.activeFormat.videoSupportedFrameRateRanges.first {
    captureSession.beginConfiguration()
    // currentCamera.activeVideoMinFrameDuration = CMTimeMake(1, Int32(frameSupportRange.maxFrameRate))
    currentCamera.activeVideoMinFrameDuration = CMTimeMake(1, YOUR_FPS_RATE)
    captureSession.commitConfiguration()
}