recently, I used AVFoundation framework to add water mark to my video, and then export the new video by AVAssetExportSession. The link below show the method and detail. https://developer.apple.com/library/content/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/03_Editing.html#//apple_ref/doc/uid/TP40010188-CH8-SW1
But the speed of export is too slow. it will cost about 20 seconds to export a water marked video which is 1 minute length in iPhone 6sp. Does anyone know how to export quickly?
PS: I try to use preset AVAssetExportPresetPassThrough in AVAssetExportSession. It costs smaller time, but my water mark is gone.