avcodec/mpegvideo: set codec tags in ff_mpv_decode_init()

Fixes Ticket3912
Reviewed-by: Benoit Fouet <benoit.fouet@free.fr>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo.c

@@ -1119,6 +1119,10 @@ void ff_mpv_decode_init(MpegEncContext *s, AVCodecContext *avctx)
     s->flags           = avctx->flags;
     s->flags2          = avctx->flags2;
 
+    /* convert fourcc to upper case */
+    s->codec_tag          = avpriv_toupper4(avctx->codec_tag);
+
+    s->stream_codec_tag   = avpriv_toupper4(avctx->stream_codec_tag);
 }
 
 static int init_er(MpegEncContext *s)
@@ -1331,10 +1335,6 @@ av_cold int ff_mpv_common_init(MpegEncContext *s)
                                   &s->chroma_x_shift,
                                   &s->chroma_y_shift);
 
-    /* convert fourcc to upper case */
-    s->codec_tag          = avpriv_toupper4(s->avctx->codec_tag);
-
-    s->stream_codec_tag   = avpriv_toupper4(s->avctx->stream_codec_tag);
 
     FF_ALLOCZ_OR_GOTO(s->avctx, s->picture,
                       MAX_PICTURE_COUNT * sizeof(Picture), fail);