[FFmpeg-devel,v7,7/8] avcodec/cbs_h2645: add helper functions to insert and delete SEI PREFIX messages

diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
index 5f71d80584..2fc957dc27 100644
--- a/libavcodec/cbs_h2645.c
+++ b/libavcodec/cbs_h2645.c
@@ -1612,3 +1612,96 @@  void ff_cbs_h264_delete_sei_message(CodedBitstreamContext *ctx,
                 (sei->payload_count - position) * sizeof(*sei->payload));
     }
 }
+
+int ff_cbs_h265_add_sei_prefix_message(CodedBitstreamContext *ctx,
+                                CodedBitstreamFragment *au,
+                                H265RawSEIPayload *payload)
+{
+    H265RawSEI *sei = NULL;
+    int err, i;
+
+    // Find an existing SEI PREFIX NAL unit to add to.
+    for (i = 0; i < au->nb_units; i++) {
+        if (au->units[i].type == HEVC_NAL_SEI_PREFIX) {
+            sei = au->units[i].content;
+            if (sei->payload_count < H265_MAX_SEI_PAYLOADS)
+                break;
+
+            sei = NULL;
+        }
+    }
+
+    if (!sei) {
+        // Need to make a new SEI NAL unit.  Insert it before the first
+        // slice data NAL unit; if no slice data, add at the end.
+        AVBufferRef *sei_ref;
+
+        sei = av_mallocz(sizeof(*sei));
+        if (!sei) {
+            err = AVERROR(ENOMEM);
+            goto fail;
+        }
+
+        sei->nal_unit_header.nal_unit_type = HEVC_NAL_SEI_PREFIX;
+        sei->nal_unit_header.nuh_layer_id = 0;
+        sei->nal_unit_header.nuh_temporal_id_plus1 = 1;
+
+        sei_ref = av_buffer_create((uint8_t*)sei, sizeof(*sei),
+                                   &cbs_h265_free_sei, NULL, 0);
+        if (!sei_ref) {
+            av_freep(&sei);
+            err = AVERROR(ENOMEM);
+            goto fail;
+        }
+
+        for (i = 0; i < au->nb_units; i++) {
+            if (au->units[i].type == HEVC_NAL_IDR_W_RADL ||
+                au->units[i].type == HEVC_NAL_IDR_N_LP)
+                break;
+        }
+
+        err = ff_cbs_insert_unit_content(ctx, au, i, HEVC_NAL_SEI_PREFIX,
+                                         sei, sei_ref);
+        av_buffer_unref(&sei_ref);
+        if (err < 0)
+            goto fail;
+    }
+
+    memcpy(&sei->payload[sei->payload_count], payload, sizeof(*payload));
+    ++sei->payload_count;
+
+    return 0;
+fail:
+    cbs_h265_free_sei_payload(payload);
+    return err;
+}
+
+void ff_cbs_h265_delete_sei_prefix_message(CodedBitstreamContext *ctx,
+                                    CodedBitstreamFragment *au,
+                                    CodedBitstreamUnit *nal,
+                                    int position)
+{
+    H265RawSEI *sei = nal->content;
+
+    av_assert0(nal->type == HEVC_NAL_SEI_PREFIX);
+    av_assert0(position >= 0 && position < sei->payload_count);
+
+    if (position == 0 && sei->payload_count == 1) {
+        // Deleting NAL unit entirely.
+        int i;
+
+        for (i = 0; i < au->nb_units; i++) {
+            if (&au->units[i] == nal)
+                break;
+        }
+
+        ff_cbs_delete_unit(ctx, au, i);
+    } else {
+        cbs_h265_free_sei_payload(&sei->payload[position]);
+
+        --sei->payload_count;
+        memmove(sei->payload + position,
+                sei->payload + position + 1,
+                (sei->payload_count - position) * sizeof(*sei->payload));
+    }
+}
diff --git a/libavcodec/cbs_h265.h b/libavcodec/cbs_h265.h
index ad746bf35f..b7e7dff658 100644
--- a/libavcodec/cbs_h265.h
+++ b/libavcodec/cbs_h265.h
@@ -22,6 +22,7 @@ 
 #include <stddef.h>
 #include <stdint.h>
 
+#include "cbs.h"
 #include "cbs_h2645.h"
 #include "hevc.h"
 
@@ -745,5 +746,29 @@  typedef struct CodedBitstreamH265Context {
     const H265RawPPS *active_pps;
 } CodedBitstreamH265Context;
 
+/**
+ * Add an SEI message to an access unit.
+ *
+ * On success, the payload will be owned by a unit in access_unit;
+ * on failure, the content of the payload will be freed.
+ */
+int ff_cbs_h265_add_sei_prefix_message(CodedBitstreamContext *ctx,
+                                CodedBitstreamFragment *access_unit,
+                                H265RawSEIPayload *payload);
+
+/**
+ * Delete an SEI message from an access unit.
+ *
+ * Deletes from nal_unit, which must be an SEI PREFIX NAL unit.  If this is the
+ * last message in nal_unit, also deletes it from access_unit.
+ *
+ * Requires nal_unit to be a unit in access_unit and position to be >= 0
+ * and < the payload count of the SEI nal_unit.
+ */
+void ff_cbs_h265_delete_sei_prefix_message(CodedBitstreamContext *ctx,
+                                    CodedBitstreamFragment *access_unit,
+                                    CodedBitstreamUnit *nal_unit,
+                                    int position);
+
 
 #endif /* AVCODEC_CBS_H265_H */