Swift：一種尺寸的視頻記錄，但呈現的大小錯誤

Question

目標是使用Swift在設備上捕獲全屏視頻。 在下面的代碼中，視頻捕獲似乎全屏發生（錄制相機預覽時使用全屏），但視頻的渲染以不同的分辨率發生。 特別是對於5S，看起來捕獲發生在320x568但渲染發生在320x480 。

如何捕獲和呈現全屏視頻？

視頻捕獲代碼：

private func initPBJVision() {
    // Store PBJVision in var for convenience
    let vision = PBJVision.sharedInstance()

    // Configure PBJVision
    vision.delegate = self
    vision.cameraMode = PBJCameraMode.Video
    vision.cameraOrientation = PBJCameraOrientation.Portrait
    vision.focusMode = PBJFocusMode.ContinuousAutoFocus
    vision.outputFormat = PBJOutputFormat.Preset
    vision.cameraDevice = PBJCameraDevice.Back

    // Let taps start/pause recording
    let tapHandler = UITapGestureRecognizer(target: self, action: "doTap:")
    view.addGestureRecognizer(tapHandler)

    // Log status
    print("Configured PBJVision")
}


private func startCameraPreview() {
    // Store PBJVision in var for convenience
    let vision = PBJVision.sharedInstance()

    // Connect PBJVision camera preview to <videoView>
    // -- Get preview width
    let deviceWidth = CGRectGetWidth(view.frame)
    let deviceHeight = CGRectGetHeight(view.frame)

    // -- Configure PBJVision's preview layer
    let previewLayer = vision.previewLayer
    previewLayer.frame = CGRectMake(0, 0, deviceWidth, deviceHeight)
    previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
    ...
}

視頻呈現代碼：

func exportVideo(fileUrl: NSURL) {
    // Create main composition object
    let videoAsset = AVURLAsset(URL: fileUrl, options: nil)
    let mainComposition = AVMutableComposition()
    let compositionVideoTrack = mainComposition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))
    let compositionAudioTrack = mainComposition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))

    // -- Extract and apply video & audio tracks to composition
    let sourceVideoTrack = videoAsset.tracksWithMediaType(AVMediaTypeVideo)[0]
    let sourceAudioTrack = videoAsset.tracksWithMediaType(AVMediaTypeAudio)[0]
    do {
        try compositionVideoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), ofTrack: sourceVideoTrack, atTime: kCMTimeZero)
    } catch {
        print("Error with insertTimeRange. Video error: \(error).")
    }
    do {
        try compositionAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), ofTrack: sourceAudioTrack, atTime: kCMTimeZero)
    } catch {
        print("Error with insertTimeRange. Audio error: \(error).")
    }

    // Add text to video
    // -- Create video composition object
    let renderSize = compositionVideoTrack.naturalSize
    let videoComposition = AVMutableVideoComposition()
    videoComposition.renderSize = renderSize
    videoComposition.frameDuration = CMTimeMake(Int64(1), Int32(videoFrameRate))

    // -- Add instruction to  video composition object
    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
    let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: compositionVideoTrack)
    instruction.layerInstructions = [videoLayerInstruction]
    videoComposition.instructions = [instruction]

    // -- Define video frame
    let videoFrame = CGRectMake(0, 0, renderSize.width, renderSize.height)
    print("Video Frame: \(videoFrame)")  // <-- Prints frame of 320x480 so render size already wrong here 
    ...

Answer 1

如果我找對你，似乎你誤解了設備屏幕寬度等於相機預覽（和捕捉）大小的事實。

該videoGravity你的財產previewLayer指示如何伸展/適合您的層內的預覽。 它不會影響捕獲輸出。

輸出的實際幀大小取決於當前AVCaptureSession sessionPreset屬性。 正如我通過閱讀PBJVision lib的GitHub存儲庫可以理解的那樣，它的單例具有這個的setter（稱為captureSessionPreset ）。 您可以在initPBJVision方法中更改它。

在那里，您可以找到會話預設的可能值。

Answer 2

試試SDAVAssetExportSession

你可以指定AVVideoWidthKey和AVVideoHeightKey你也可以指定配置文件， AVVideoProfileLevelKey即AVVideoProfileLevelH264HighAutoLevel用於支持4k的東西，朋友（Michael Lowin）跟蹤該屬性以幫助我們提高一些出口品質。