Exporting time lapse with AVAssetExportSession results in black video

Question

I need to be able to merge videos taken with the time lapse function in the Camera app on iOS and export as a single video.

However, even if I try to export a singl

Answer 1

The problem code is:

videoLayerInstruction.setTransform(videoAssetTrack!.preferredTransform, at: kCMTimeZero)

This transformation is eligible to "up" (default) orientation only and it makes a video completely black for the other orientations. You should make a correct transformation for each orientation e.g.:

var transform = videoAssetTrack.preferredTransform
// Right
if transform.a == 0 && transform.b == 1.0 && transform.c == -1.0 && transform.d == 0 {
    isPortrait = true
    let rotate = CGAffineTransform.identity.translatedBy(x: videoAssetTrack.naturalSize.height - videoAssetTrack.preferredTransform.tx, y: -videoAssetTrack.preferredTransform.ty)
    transform = videoAssetTrack.preferredTransform.concatenating(rotate)
}
// Left
else if transform.a == 0 && transform.b == -1.0 && transform.c == 1.0 && transform.d == 0 {
    isPortrait = true
    let rotate = CGAffineTransform.identity.translatedBy(x:  -videoAssetTrack.preferredTransform.tx, y: videoAssetTrack.naturalSize.width - videoAssetTrack.preferredTransform.ty)
    transform = videoAssetTrack.preferredTransform.concatenating(rotate)
}
// Up
else if transform.a == 1.0 && transform.b == 0 && transform.c == 0 && transform.d == 1.0 {
    transform = videoAssetTrack.preferredTransform
}
// Down
else if transform.a == -1.0 && transform.b == 0 && transform.c == 0 && transform.d == -1.0 {
    let rotate = CGAffineTransform.identity.translatedBy(x: videoAssetTrack.naturalSize.width - videoAssetTrack.preferredTransform.tx, y: videoAssetTrack.naturalSize.height - videoAssetTrack.preferredTransform.ty)
    transform = videoAssetTrack.preferredTransform.concatenating(rotate)
}

videoLayerInstruction.setTransform(transform, at: .zero)