I'm trying to decode a prores4444 video with alpha channel on iOS with Swift to overlay as a complex animation over a user video and to export it to his library. The AVFoundation documentation is not that great and I'm struggling to find any code examples.
When I try to use the code below with AVAssetReaderTrackOutput to decode the video I get an "AVAssetReaderOutput does not currently support compressed output" error.
let avAssetReaderVideoCompositionOutput = AVAssetReaderVideoCompositionOutput(videoTracks: [videoOverlayAssetTrack], videoSettings: outputSettings: [AVVideoCodecKey: AVVideoCodecType.proRes4444])
Does anyone have a clue how to read in an asset track of a prores4444 with alpha channel to use it for an instance of AVMutableVideoCompositionLayerInstruction?
Should I use another codec?
来源：https://stackoverflow.com/questions/47627605/avfoundation-decode-prores4444-movie-with-alpha-channel