Improve codec_tag guessing code.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -25,6 +25,7 @@
 #include "avio_internal.h"
 #include "internal.h"
 #include "libavcodec/internal.h"
+#include "libavcodec/raw.h"
 #include "libavutil/opt.h"
 #include "metadata.h"
 #include "id3v2.h"
@@ -2428,8 +2429,11 @@ int av_find_stream_info(AVFormatContext *ic)
                      (st->codec_info_nb_frames-2)*(int64_t)st->time_base.den,
                       st->info->codec_info_duration*(int64_t)st->time_base.num, 60000);
         if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
-            if(st->codec->codec_id == CODEC_ID_RAWVIDEO && !st->codec->codec_tag && !st->codec->bits_per_coded_sample)
-                st->codec->codec_tag= avcodec_pix_fmt_to_codec_tag(st->codec->pix_fmt);
+            if(st->codec->codec_id == CODEC_ID_RAWVIDEO && !st->codec->codec_tag && !st->codec->bits_per_coded_sample){
+                uint32_t tag= avcodec_pix_fmt_to_codec_tag(st->codec->pix_fmt);
+                if(ff_find_pix_fmt(ff_raw_pix_fmt_tags, tag) == st->codec->pix_fmt)
+                    st->codec->codec_tag= tag;
+            }
 
             // the check for tb_unreliable() is not completely correct, since this is not about handling
             // a unreliable/inexact time base, but a time base that is finer than necessary, as e.g.