从UnsafeRawPointer转换为CFMutableDictionary失败

Question

我遇到了类似问题的问题：Why AVSampleBufferDisplayLayer stops showing CMSampleBuffers taken from AVCaptureVideoDataOutput's delegate?

并尝试了这个问题的建议。

但是当我粘贴这段代码时：

let attachments: CFArray = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true)!;

    print(CFArrayGetCount(attachments)) // printing 1

    let dict = CFArrayGetValueAtIndex(attachments, 0) as! CFMutableDictionary;

    CFDictionarySetValue(dict,
                         unsafeBitCast(kCMSampleAttachmentKey_DisplayImmediately, to: UnsafeRawPointer.self),
                         unsafeBitCast(kCFBooleanTrue, to: UnsafeRawPointer.self));

应用程序在转换为CFMutableDictionary时崩溃。

我做错了什么？