ff_framesync_dualinput_get_writable  298 libavfilter/framesync.h int ff_framesync_dualinput_get_writable(FFFrameSync *fs, AVFrame **f0, AVFrame **f1);
ff_framesync_dualinput_get_writable  938 libavfilter/vf_overlay.c     ret = ff_framesync_dualinput_get_writable(fs, &mainpic, &second);
ff_framesync_dualinput_get_writable 1019 libavfilter/vf_paletteuse.c     ret = ff_framesync_dualinput_get_writable(fs, &master, &second);