h264_mp4toannexb: Copy one NAL unit at a time

If processing an input NAL unit triggers the insertion of data from
extradata in front of said NAL unit, the output packet is grown (i.e.
reallocated) once to accomodate both the new extradata as well as the
input NAL unit itself; this has been changed: In such a situation, the
packet is now grown twice. While this is bad for performance, it allows
to simplify the code and ultimately to stop reallocating the packet
altogether.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h264_mp4toannexb_bsf.c

@@ -43,26 +43,23 @@ typedef struct H264BSFContext {
 } H264BSFContext;
 
 static int alloc_and_copy(AVPacket *out,
-                          const uint8_t *sps_pps, uint32_t sps_pps_size,
                           const uint8_t *in, uint32_t in_size, int ps)
 {
     uint32_t offset         = out->size;
-    uint8_t start_code_size = offset == 0 && sps_pps_size == 0 || ps ? 4 : 3;
+    uint8_t start_code_size = ps < 0 ? 0 : offset == 0 || ps ? 4 : 3;
     int err;
 
-    err = av_grow_packet(out, sps_pps_size + in_size + start_code_size);
+    err = av_grow_packet(out, in_size + start_code_size);
     if (err < 0)
         return err;
 
-    if (sps_pps)
-        memcpy(out->data + offset, sps_pps, sps_pps_size);
-    memcpy(out->data + sps_pps_size + start_code_size + offset, in, in_size);
+    memcpy(out->data + start_code_size + offset, in, in_size);
     if (start_code_size == 4) {
-        AV_WB32(out->data + offset + sps_pps_size, 1);
-    } else {
-        (out->data + offset + sps_pps_size)[0] =
-        (out->data + offset + sps_pps_size)[1] = 0;
-        (out->data + offset + sps_pps_size)[2] = 1;
+        AV_WB32(out->data + offset, 1);
+    } else if (start_code_size) {
+        (out->data + offset)[0] =
+        (out->data + offset)[1] = 0;
+        (out->data + offset)[2] = 1;
     }
 
     return 0;
@@ -226,10 +223,9 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *out)
                     if ((ret = alloc_and_copy(out,
                                          s->sps,
                                          s->sps_size,
-                                         buf, nal_size, 1)) < 0)
+                                         -1)) < 0)
                         goto fail;
                     s->idr_sps_seen = 1;
-                    goto next_nal;
                 }
             }
         }
@@ -242,32 +238,29 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *out)
 
         /* prepend only to the first type 5 NAL unit of an IDR picture, if no sps/pps are already present */
         if (s->new_idr && unit_type == H264_NAL_IDR_SLICE && !s->idr_sps_seen && !s->idr_pps_seen) {
-            if ((ret=alloc_and_copy(out,
+            if (ctx->par_out->extradata && (ret=alloc_and_copy(out,
                                ctx->par_out->extradata, ctx->par_out->extradata_size,
-                               buf, nal_size, 0)) < 0)
+                               -1)) < 0)
                 goto fail;
             s->new_idr = 0;
         /* if only SPS has been seen, also insert PPS */
         } else if (s->new_idr && unit_type == H264_NAL_IDR_SLICE && s->idr_sps_seen && !s->idr_pps_seen) {
             if (!s->pps_size) {
                 av_log(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable\n");
-                if ((ret = alloc_and_copy(out, NULL, 0, buf, nal_size, 0)) < 0)
-                    goto fail;
             } else if ((ret = alloc_and_copy(out,
                                         s->pps, s->pps_size,
-                                        buf, nal_size, 0)) < 0)
+                                        -1)) < 0)
                 goto fail;
-        } else {
-            if ((ret=alloc_and_copy(out, NULL, 0, buf, nal_size, unit_type == H264_NAL_SPS || unit_type == H264_NAL_PPS)) < 0)
+        }
+
+            if ((ret=alloc_and_copy(out, buf, nal_size, unit_type == H264_NAL_SPS || unit_type == H264_NAL_PPS)) < 0)
                 goto fail;
             if (!s->new_idr && unit_type == H264_NAL_SLICE) {
                 s->new_idr = 1;
                 s->idr_sps_seen = 0;
                 s->idr_pps_seen = 0;
             }
-        }
 
-next_nal:
         buf        += nal_size;
         cumul_size += nal_size + s->length_size;
     } while (cumul_size < buf_size);