更新到Xcode 9.0 final之后，我无法构建我的Objective-C项目。它说：
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS11.0.sdk/System/Library/Frameworks/AVFoundation.framework/Headers/AVMediaFormat.h:14:20: Typedef redefinition with different types ('NSString *' vs 'AVMediaType')
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS11.0.sdk/System/Library/Frameworks/AVFoundation.framework/Headers/AVAssetWriter.h:135:41: Type argument 'AVMediaType' is neither an Objective-C object nor a block type
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS11.0.sdk/System/Library/Frameworks/AVFoundation.framework/Headers/AVCaptureDevice.h:513:102: Nullability specifier 'nullable' cannot be applied to non-pointer type 'AVMediaType'
答案 0 :(得分：0)
您需要在项目中查看使用AVMediaType的位置，例如使用ffmpeg库并重命名＆＃39; AVMediaType＆＃39;在ffmpeg中引用的其他地方，如avutil.h中的avformat.h avcodec.h等。