avcodec/h264: Keep a reference to the last picture for EC

This and the next commit improve error concealment for
green-block-artifacts-from-canon-100-hs.MOV
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -1838,6 +1838,8 @@ static int h264_decode_frame(AVCodecContext *avctx, void *data,
      * packets do not get used. */
     h->data_partitioning = 0;
 
+    ff_h264_unref_picture(h, &h->last_pic_for_ec);
+
     /* end of stream, output what is still in the buffers */
     if (buf_size == 0) {
  out:
@@ -1930,6 +1932,8 @@ static int h264_decode_frame(AVCodecContext *avctx, void *data,
 
     assert(pict->buf[0] || !*got_frame);
 
+    ff_h264_unref_picture(h, &h->last_pic_for_ec);
+
     return get_consumed_bytes(buf_index, buf_size);
 }
 
@@ -1954,6 +1958,7 @@ static av_cold int h264_decode_end(AVCodecContext *avctx)
     ff_h264_free_context(h);
 
     ff_h264_unref_picture(h, &h->cur_pic);
+    ff_h264_unref_picture(h, &h->last_pic_for_ec);
 
     return 0;
 }

libavcodec/h264.h

@@ -352,6 +352,7 @@ typedef struct H264Context {
     H264Picture *DPB;
     H264Picture *cur_pic_ptr;
     H264Picture cur_pic;
+    H264Picture last_pic_for_ec;
 
     int pixel_shift;    ///< 0 for 8-bit H264, 1 for high-bit-depth H264
     int chroma_qp[2];   // QPc

libavcodec/h264_refs.c

@@ -493,6 +493,10 @@ void ff_h264_remove_all_refs(H264Context *h)
     }
     assert(h->long_ref_count == 0);
 
+    ff_h264_unref_picture(h, &h->last_pic_for_ec);
+    if (h->short_ref_count)
+        ff_h264_ref_picture(h, &h->last_pic_for_ec, h->short_ref[0]);
+
     for (i = 0; i < h->short_ref_count; i++) {
         unreference_pic(h, h->short_ref[i], 0);
         h->short_ref[i] = NULL;

libavcodec/h264_slice.c

@@ -542,6 +542,7 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
         memset(&h->mb_luma_dc, 0, sizeof(h->mb_luma_dc));
         memset(&h->mb_padding, 0, sizeof(h->mb_padding));
         memset(&h->cur_pic, 0, sizeof(h->cur_pic));
+        memset(&h->last_pic_for_ec, 0, sizeof(h->last_pic_for_ec));
 
         h->avctx             = dst;
         h->DPB               = NULL;
@@ -1959,7 +1960,12 @@ int ff_h264_decode_slice_header(H264Context *h, H264Context *h0)
                              (h->ref_list[j][i].reference & 3);
     }
 
-    if (h->ref_count[0]) ff_h264_set_erpic(&h->er.last_pic, &h->ref_list[0][0]);
+    if (h->ref_count[0]) {
+        ff_h264_set_erpic(&h->er.last_pic, &h->ref_list[0][0]);
+    } else if (h->last_pic_for_ec.f.buf[0]) {
+        ff_h264_set_erpic(&h->er.last_pic, &h->last_pic_for_ec);
+    }
+
     if (h->ref_count[1]) ff_h264_set_erpic(&h->er.next_pic, &h->ref_list[1][0]);
 
     h->er.ref_count = h->ref_count[0];