Looks like ffmpeg AVFrame width/height/format for the deinterlaced frame was never initialized. That was not a problem until starting with 4.1 the colorspace conversion and upside down flip was started to be multi-threaded, which accessed the frame width/height. Also, the memory storage for the deinterlaced frame was never freed either; fix that too. Pull Request: https://projects.blender.org/blender/blender/pulls/127689