那自己回答吧,不知道为什么，只有异步才成功。不知道是不是线程的问题。有知道答案的人分析一下么
贴一下成功的代码

```swift

func signIn4() {
Task {
do {
let cOntent= try await getShareableContent()
guard let display = content.displays.first else { return }
print(display)
let filter = SCContentFilter(display: display, excludingWindows: [])
let cOnfig= SCStreamConfiguration()
config.minimumFrameInterval = CMTime(value: 1, timescale: 10)
let stream = SCStream(filter: filter, configuration: config, delegate: nil)
let output = Output()
try stream.addStreamOutput(output, type: .screen, sampleHandlerQueue: nil)
try await stream.startCapture()
try await Task.sleep(nanoseconds: 200_000_000)
try await stream.stopCapture()
} catch {
print("Failed to retrieve capturable content or start stream: \(error.localizedDescription)")
}
}
}

func getShareableContent() async throws -> SCShareableContent {
return try await withCheckedThrowingContinuation { continuation in
SCShareableContent.getWithCompletionHandler { content, error in
if let error = error {
continuation.resume(throwing: error)
} else if let cOntent= content {
continuation.resume(returning: content)
}
}
}
}

```