Revert "Revert "Merge commit 'd1d76780'""

This reverts commit e4af9be0 and redoes
796027f2.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h264_slice.c

@@ -1497,6 +1497,8 @@ static int h264_field_start(H264Context *h, const H264SliceContext *sl,
     h->nb_mmco = sl->nb_mmco;
     h->explicit_ref_marking = sl->explicit_ref_marking;
 
+    h->picture_idr = nal->type == H264_NAL_IDR_SLICE;
+
     /* Set the frame properties/side data. Only done for the second field in
      * field coded frames, since some SEI information is present for each field
      * and is merged by the SEI parsing code. */
@@ -1829,6 +1831,11 @@ int ff_h264_decode_slice_header(H264Context *h, H264SliceContext *sl,
         }
     }
 
+    if (h->picture_idr && nal->type != H264_NAL_IDR_SLICE) {
+        av_log(h->avctx, AV_LOG_ERROR, "Invalid mix of IDR and non-IDR slices\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     av_assert1(h->mb_num == h->mb_width * h->mb_height);
     if (sl->first_mb_addr << FIELD_OR_MBAFF_PICTURE(h) >= h->mb_num ||
         sl->first_mb_addr >= h->mb_num) {

libavcodec/h264dec.c

@@ -783,12 +783,6 @@ again:
                 ret = -1;
                 goto end;
             }
-            if (nal->type != H264_NAL_IDR_SLICE) {
-                av_log(h->avctx, AV_LOG_ERROR,
-                       "Invalid mix of idr and non-idr slices\n");
-                ret = -1;
-                goto end;
-            }
             if(!idr_cleared) {
                 if (h->current_slice && (avctx->active_thread_type & FF_THREAD_SLICE)) {
                     av_log(h, AV_LOG_ERROR, "invalid mixed IDR / non IDR frames cannot be decoded in slice multithreading mode\n");

libavcodec/h264dec.h

@@ -384,6 +384,11 @@ typedef struct H264Context {
      */
     int postpone_filter;
 
+    /*
+     * Set to 1 when the current picture is IDR, 0 otherwise.
+     */
+    int picture_idr;
+
     int8_t(*intra4x4_pred_mode);
     H264PredContext hpc;