cbs_h2645: Avoid memcpy when splitting fragment

Now memcpy is avoided for NAL units that don't contain 0x03 escape
characters.

Improves performance of cbs_h2645_fragment_add_nals from 36940
decicycles to 6364 decicycles based on 8 runs with a 5.1 Mb/s H.264
sample (262144 runs each).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@googlemail.com>
Signed-off-by: Mark Thompson <sw@jkqxz.net>

libavcodec/cbs_h2645.c

@@ -532,24 +532,30 @@ static int cbs_h2645_fragment_add_nals(CodedBitstreamContext *ctx,
     for (i = 0; i < packet->nb_nals; i++) {
         const H2645NAL *nal = &packet->nals[i];
         size_t size = nal->size;
-        uint8_t *data;
 
         // Remove trailing zeroes.
         while (size > 0 && nal->data[size - 1] == 0)
             --size;
         av_assert0(size > 0);
 
-        data = av_malloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
-        if (!data)
-            return AVERROR(ENOMEM);
-        memcpy(data, nal->data, size);
-        memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
+        if (nal->data == nal->raw_data) {
+            err = ff_cbs_insert_unit_data(ctx, frag, -1, nal->type,
+                                (uint8_t*)nal->data, size, frag->data_ref);
+            if (err < 0)
+                return err;
+        } else {
+            uint8_t *data = av_malloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
+            if (!data)
+                return AVERROR(ENOMEM);
+            memcpy(data, nal->data, size);
+            memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
 
-        err = ff_cbs_insert_unit_data(ctx, frag, -1, nal->type,
-                                      data, size, NULL);
-        if (err < 0) {
-            av_freep(&data);
-            return err;
+            err = ff_cbs_insert_unit_data(ctx, frag, -1, nal->type,
+                                          data, size, NULL);
+            if (err < 0) {
+                av_freep(&data);
+                return err;
+            }
         }
     }
 

libavcodec/h2645_parse.h

@@ -86,6 +86,12 @@ int ff_h2645_extract_rbsp(const uint8_t *src, int length, H2645RBSP *rbsp,
 
 /**
  * Split an input packet into NAL units.
+ *
+ * If data == raw_data holds true for a NAL unit of the returned pkt, then
+ * said NAL unit does not contain any emulation_prevention_three_byte and
+ * the data is contained in the input buffer pointed to by buf.
+ * Otherwise, the unescaped data is part of the rbsp_buffer described by the
+ * packet's H2645RBSP.
  */
 int ff_h2645_packet_split(H2645Packet *pkt, const uint8_t *buf, int length,
                           void *logctx, int is_nalff, int nal_length_size,