Swift VTCompressionSession的输出回调未运行

我一直在使用VideoToolBox对视频数据进行编码，但我无法获得运行我正在运行的

VTCompressionSession

的回调

下面是我如何声明

VTCompressionSession

VTCompressionSessionCreate(allocator: nil,
width: 1080, height: 1920,
codecType: kCMVideoCodecType_H264,
encoderSpecification: nil, imageBufferAttributes: nil,
compressedDataAllocator: nil,
outputCallback: compressionOutputCallback as? VTCompressionOutputCallback, refcon: nil,
compressionSessionOut: sessionOut)

这是我的输出回调

func compressionOutputCallback(
        outputCallbackRefCon:UnsafeMutableRawPointer?,
        sourceFrameRefCon:UnsafeMutableRawPointer?,
        status:OSStatus,
        infoFlags:VTEncodeInfoFlags,
        sampleBuffer:CMSampleBuffer) {

        //Do stuff with CMSampleBuffer


        if status != noErr{
            NSLog("SBC: Error encoding video", status)

            print("SBC: Error encoding video", status)

            return

        }

        print("SBC: compressionOutputCallback dataBuffer", status)

    }

但是日志显示回调没有运行，即使我为

VTCompressionSession

指定了回调

我对Swift一般来说是新手，特别是对VideoToolBox，所以非常感谢大家在这方面的帮助