mpeg12: more advanced ffmpeg mpeg2 aspect guessing code.

Fixes issue1613, 621, 562 simultaneously
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/mpeg12.c

@@ -1293,9 +1293,17 @@ static int mpeg_decode_postinit(AVCodecContext *avctx){
             avctx->ticks_per_frame=2;
         //MPEG-2 aspect
             if(s->aspect_ratio_info > 1){
-                //we ignore the spec here as reality does not match the spec, see for example
+                AVRational dar =
+                    av_mul_q(
+                        av_div_q(ff_mpeg2_aspect[s->aspect_ratio_info],
+                                 (AVRational){s1->pan_scan.width, s1->pan_scan.height}),
+                        (AVRational){s->width, s->height});
+
+                // we ignore the spec here and guess a bit as reality does not match the spec, see for example
                 // res_change_ffmpeg_aspect.ts and sequence-display-aspect.mpg
-                if( (s1->pan_scan.width == 0 )||(s1->pan_scan.height == 0) || 1){
+                // issue1613, 621, 562
+                if((s1->pan_scan.width == 0 ) || (s1->pan_scan.height == 0) ||
+                   (av_cmp_q(dar,(AVRational){4,3}) && av_cmp_q(dar,(AVRational){16,9}))) {
                     s->avctx->sample_aspect_ratio=
                         av_div_q(
                          ff_mpeg2_aspect[s->aspect_ratio_info],
@@ -1307,6 +1315,12 @@ static int mpeg_decode_postinit(AVCodecContext *avctx){
                          ff_mpeg2_aspect[s->aspect_ratio_info],
                          (AVRational){s1->pan_scan.width, s1->pan_scan.height}
                         );
+//issue1613 4/3 16/9 -> 16/9
+//res_change_ffmpeg_aspect.ts 4/3 225/44 ->4/3
+//widescreen-issue562.mpg 4/3 16/9 -> 16/9
+//                    s->avctx->sample_aspect_ratio= av_mul_q(s->avctx->sample_aspect_ratio, (AVRational){s->width, s->height});
+//av_log(NULL, AV_LOG_ERROR, "A %d/%d\n",ff_mpeg2_aspect[s->aspect_ratio_info].num, ff_mpeg2_aspect[s->aspect_ratio_info].den);
+//av_log(NULL, AV_LOG_ERROR, "B %d/%d\n",s->avctx->sample_aspect_ratio.num, s->avctx->sample_aspect_ratio.den);
                 }
             }else{
                 s->avctx->sample_aspect_ratio=