h264: Support SMV2

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

libavcodec/h264_ps.c

@@ -429,6 +429,8 @@ int ff_h264_decode_seq_parameter_set(H264Context *h){
     }
 
     sps->ref_frame_count= get_ue_golomb_31(&s->gb);
+    if (h->s.avctx->codec_tag == MKTAG('S', 'M', 'V', '2'))
+        sps->ref_frame_count= 2;
     if(sps->ref_frame_count > MAX_PICTURE_COUNT-2 || sps->ref_frame_count > 16U){
         av_log(h->s.avctx, AV_LOG_ERROR, "too many reference frames\n");
         goto fail;