sh->disp_w and sh->disp_h, otherwise it will break when the
resolution changes mid-stream, like in
http://samples.mplayerhq.hu/MPEG2/res_change_ffmpeg_aspect.ts
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@20687 b3059339-0415-0410-9bf9-f77b7e298cf2