diff --git a/libavcodec/h264_sei.c b/libavcodec/h264_sei.c
index 6499086210..43593d34d2 100644
--- a/libavcodec/h264_sei.c
+++ b/libavcodec/h264_sei.c
@@ -51,8 +51,7 @@ void ff_h264_sei_uninit(H264SEIContext *h)
     h->display_orientation.present = 0;
     h->afd.present                 =  0;
 
-    h->a53_caption.a53_caption_size = 0;
-    av_freep(&h->a53_caption.a53_caption);
+    av_buffer_unref(&h->a53_caption.buf_ref);
 }
 
 static int decode_picture_timing(H264SEIPictureTiming *h, GetBitContext *gb,
@@ -169,7 +168,8 @@ static int decode_registered_user_data_closed_caption(H264SEIA53Caption *h,
             size -= 2;
 
             if (cc_count && size >= cc_count * 3) {
-                const uint64_t new_size = (h->a53_caption_size + cc_count
+                int old_size = h->buf_ref ? h->buf_ref->size : 0;
+                const uint64_t new_size = (old_size + cc_count
                                            * UINT64_C(3));
                 int i, ret;
 
@@ -177,14 +177,15 @@ static int decode_registered_user_data_closed_caption(H264SEIA53Caption *h,
                     return AVERROR(EINVAL);
 
                 /* Allow merging of the cc data from two fields. */
-                ret = av_reallocp(&h->a53_caption, new_size);
+                ret = av_buffer_realloc(&h->buf_ref, new_size);
                 if (ret < 0)
                     return ret;
 
+                /* Use of av_buffer_realloc assumes buffer is writeable */
                 for (i = 0; i < cc_count; i++) {
-                    h->a53_caption[h->a53_caption_size++] = get_bits(gb, 8);
-                    h->a53_caption[h->a53_caption_size++] = get_bits(gb, 8);
-                    h->a53_caption[h->a53_caption_size++] = get_bits(gb, 8);
+                    h->buf_ref->data[old_size++] = get_bits(gb, 8);
+                    h->buf_ref->data[old_size++] = get_bits(gb, 8);
+                    h->buf_ref->data[old_size++] = get_bits(gb, 8);
                 }
 
                 skip_bits(gb, 8);   // marker_bits
diff --git a/libavcodec/h264_sei.h b/libavcodec/h264_sei.h
index a169a10e49..5b7c8ef9d8 100644
--- a/libavcodec/h264_sei.h
+++ b/libavcodec/h264_sei.h
@@ -95,8 +95,7 @@ typedef struct H264SEIAFD {
 } H264SEIAFD;
 
 typedef struct H264SEIA53Caption {
-    int a53_caption_size;
-    uint8_t *a53_caption;
+    AVBufferRef *buf_ref;
 } H264SEIA53Caption;
 
 typedef struct H264SEIUnregistered {
diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index ede9a1a6ea..f31c9a2579 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -430,6 +430,15 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
 
     h->frame_recovered       = h1->frame_recovered;
 
+    av_buffer_unref(&h->sei.a53_caption.buf_ref);
+    h->sei.a53_caption.buf_ref = NULL;
+
+    if (h1->sei.a53_caption.buf_ref) {
+        h->sei.a53_caption.buf_ref = av_buffer_ref(h1->sei.a53_caption.buf_ref);
+        if (!h->sei.a53_caption.buf_ref)
+            return AVERROR(ENOMEM);
+    }
+
     if (!h->cur_pic_ptr)
         return 0;
 
@@ -1269,15 +1278,16 @@ static int h264_export_frame_props(H264Context *h)
         }
     }
 
-    if (h->sei.a53_caption.a53_caption) {
+    if (h->sei.a53_caption.buf_ref) {
         H264SEIA53Caption *a53 = &h->sei.a53_caption;
-        AVFrameSideData *sd = av_frame_new_side_data(cur->f,
-                                                     AV_FRAME_DATA_A53_CC,
-                                                     a53->a53_caption_size);
-        if (sd)
-            memcpy(sd->data, a53->a53_caption, a53->a53_caption_size);
-        av_freep(&a53->a53_caption);
-        a53->a53_caption_size = 0;
+
+        AVFrameSideData *sd = av_frame_new_side_data_from_buf(cur->f, AV_FRAME_DATA_A53_CC, av_buffer_ref(a53->buf_ref));
+        if (sd) {
+            av_buffer_unref(&a53->buf_ref);
+        } else {
+            return AVERROR(ENOMEM);
+        }
+
         h->avctx->properties |= FF_CODEC_PROPERTY_CLOSED_CAPTIONS;
     }
 
diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index 7494c7a8f2..8d115fa040 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -609,9 +609,10 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size)
 
     if (!(avctx->flags2 & AV_CODEC_FLAG2_CHUNKS)) {
         h->current_slice = 0;
-        if (!h->first_field)
+        if (!h->first_field) {
             h->cur_pic_ptr = NULL;
-        ff_h264_sei_uninit(&h->sei);
+            ff_h264_sei_uninit(&h->sei);
+        }
     }
 
     if (h->nal_length_size == 4) {
