AVAssetExportSession giving me a green border on right and bottom of output video

Question

Here's the code:

AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];
        exporter.outputURL = outputUrl;
        exporter.outputFileType = AVFileTypeQuickTimeMovie;
        exporter.videoComposition = mainComposition;
        exporter.shouldOptimizeForNetworkUse = YES;
        [exporter exportAsynchronouslyWithCompletionHandler:^{
            //completion
        }];

I've tried different quality settings. I always get a 1-2 pixel border running down the right side of the video and along the bottom, no matter what video I'm trying to render. What could be causing this and how do I fix it?

EDIT: I am not using any kind of green color anywhere, so this must be coming from the framework somehow.

Answer 1

Usually green lines appear after video cropping, problem is in video renderSize width, it should be multiply of 16.

Here some links about this: apple 1 apple 2

Answer 2

a much nicer solution to get the multiple of 16 would be this approach:

floor(width / 16) * 16

or

ceil(width / 16) * 16

depending on your preference of having a smaller or bigger width

Answer 3

This did the magic for me (iOS9, Swift 3, iPhone 6):

Based on: https://www.raywenderlich.com/94404/play-record-merge-videos-ios-swift

Changing mainComposition.renderSize to:

mainComposition.renderSize = CGSize(width: self.mainCompositionWidth, height: self.mainCompositionHeight)

where mainCompositionWidth, mainCompositionHeight are CGFloats and are calculated like this:

 self.mainCompositionWidth = UIScreen.mainScreen().bounds.width
    self.mainCompositionHeight = UIScreen.mainScreen().bounds.height

    while (self.mainCompositionWidth%16>0) { // find the right resolution that can be divided by 16
        self.mainCompositionWidth = self.mainCompositionWidth + 1.0
    }

    while (self.mainCompositionHeight%16>0) { // find the right resolution that can be divided by 16
        self.mainCompositionHeight = self.mainCompositionHeight + 1.0
    }

Also modifying scaleFitRatio in the videoCompositionInstructionForTrack function to:

scaleToFitRatio = self.mainCompositionWidth / assetTrack.naturalSize.height

This made the bottom green line disappear and the video fills the screen.