Also copy pixel_aspect when copying the picref in avfilter_start_frame.

This avoids a division by zero in '[in]fifo,scale[out]'

Originally committed as revision 18507 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/avfilter.c

@@ -221,6 +221,7 @@ void avfilter_start_frame(AVFilterLink *link, AVFilterPicRef *picref)
         link->cur_pic = avfilter_default_get_video_buffer(link, dst->min_perms);
         link->srcpic = picref;
         link->cur_pic->pts = link->srcpic->pts;
+        link->cur_pic->pixel_aspect = link->srcpic->pixel_aspect;
     }
     else
         link->cur_pic = picref;