Check H264 NALUs for frametype and insert SPS/PPS packets into the PacketBuffer.

webrtc/modules/video_coding/h264_sps_pps_tracker.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 19 matching lines @@
 
 H264SpsPpsTracker::PacketAction H264SpsPpsTracker::CopyAndFixBitstream(
     VCMPacket* packet) {
   RTC_DCHECK(packet->codec == kVideoCodecH264);
 
   const uint8_t* data = packet->dataPtr;
   const size_t data_size = packet->sizeBytes;
   const RTPVideoHeader& video_header = packet->video_header;
   const RTPVideoHeaderH264& codec_header = video_header.codecHeader.H264;
 
-  // Packets that only contains SPS/PPS are not decodable by themselves, and
-  // to avoid frames being created containing only these two nalus we don't
-  // insert them into the PacketBuffer. Instead we save the SPS/PPS and
-  // prepend the bitstream of first packet of an IDR referring to the
-  // corresponding SPS/PPS id.
-  bool insert_packet = codec_header.nalus_length == 0 ? true : false;
-
   int pps_id = -1;
   int sps_id = -1;
+  bool append_sps_pps = codec_header.nalus_length == 0;
   size_t required_size = 0;
   for (size_t i = 0; i < codec_header.nalus_length; ++i) {
     const NaluInfo& nalu = codec_header.nalus[i];
     switch (nalu.type) {
       case H264::NaluType::kSps: {
         // Save SPS.
         sps_data_[nalu.sps_id].size = nalu.size;
         sps_data_[nalu.sps_id].data.reset(new uint8_t[nalu.size]);
         memcpy(sps_data_[nalu.sps_id].data.get(), data + nalu.offset,
                nalu.size);
@@ skipping 35 matching lines @@
             return kRequestKeyframe;
           }
 
           pps_id = nalu.pps_id;
           required_size += pps->second.size + sizeof(start_code_h264);
           required_size += sps->second.size + sizeof(start_code_h264);
         }
         FALLTHROUGH();
       }
       default: {
-        // Something other than an SPS/PPS nalu in this packet, then it should
-        // be inserted into the PacketBuffer.
-        insert_packet = true;
+        // Something other than an SPS/PPS nalu in this packet, then the SPS/PPS
+        // should be appended.
+        append_sps_pps = true;
       }
     }
   }
 
-  if (!insert_packet)
-    return kDrop;
+  if (!append_sps_pps) {
+    // Two things: Firstly, when we receive a packet the data pointed at by
+    // |dataPtr| is volatile, meaning we have to copy the data into our own
+    // buffer if we want to use it at a later stage. Secondly, when a packet is
+    // inserted into the PacketBuffer it expects the packet to own its own
+    // buffer, and this function copies (and fix) the bitstream of the packet
+    // into its own buffer.
+    //
+    // SPS/PPS packets is a special case. Since we save the SPS/PPS NALU and
+    // append it to the first packet of every IDR frame the SPS/PPS packet
+    // doesn't actually need to contain any bitstream data.
+    packet->dataPtr = nullptr;
+    packet->sizeBytes = 0;
+    return kInsert;
+  }
 
   // Calculate how much space we need for the rest of the bitstream.
   if (codec_header.packetization_type == kH264StapA) {
     const uint8_t* nalu_ptr = data + 1;
     while (nalu_ptr < data + data_size) {
       RTC_DCHECK(video_header.is_first_packet_in_frame);
       required_size += sizeof(start_code_h264);
 
       // The first two bytes describe the length of a segment.
       uint16_t segment_length = nalu_ptr[0] << 8 | nalu_ptr[1];
@@ skipping 123 matching lines @@
   pps_info.data.reset(pps_data);
   pps_data_[parsed_pps->id] = std::move(pps_info);
 
   LOG(LS_INFO) << "Inserted SPS id " << parsed_sps->id << " and PPS id "
                << parsed_pps->id << " (referencing SPS " << parsed_pps->sps_id
                << ")";
 }
 
 }  // namespace video_coding
 }  // namespace webrtc