AVMutableComposition resizing issue

Question

I\'m trying to render an image into a video captured with the front camera using AVMutableComposition. The size of the resulting video (including the image) is

Answer 1

This is really tricky: You need to check the preferredTransform of the video track to determine wether it is a portrait video or not.

    var videoAssetOrientation = UIImageOrientation.up
    var isVideoAssetPortrait = false
    var videoTransform = videoAssetTrack.preferredTransform
    if needsMirroring == true  {
        isVideoAssetPortrait = true
    }else if videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0 {
        videoAssetOrientation = .right
        isVideoAssetPortrait = true
    }else if videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0 {
        videoAssetOrientation = .left
        isVideoAssetPortrait = true
    }else if videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0 {
        videoAssetOrientation = .up
    }else if videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0 {
        videoAssetOrientation = .down
    }

    //Add instructions
    mainInstruction.layerInstructions = [videoLayerInstruction]
    let mainCompositionInst = AVMutableVideoComposition()
    let naturalSize : CGSize!
    if isVideoAssetPortrait {
        naturalSize = CGSize(width: videoAssetTrack.naturalSize.height, height: videoAssetTrack.naturalSize.width)
    } else {
        naturalSize = videoAssetTrack.naturalSize
    }

Hope that helps.

Answer 2

Try applying a negative scale transform to flip the video when mirrored:

// Create an AvmutableVideoCompositionLayerInstruction
let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction.init(assetTrack: videoTrack!)
let flipped = videoAssetTrack.preferredTransform.scaledBy(x: -1.0, y: 1.0)
videoLayerInstruction.setTransform(flipped, at: kCMTimeZero)
compositionInstructions.layerInstructions = [videoLayerInstruction]