New H264PacketBuffer consolidating a bunch of H264 specific hacks into one class.

Bug: webrtc:12579
Change-Id: Idea35983e204e4a3f8628d5b4eb587bbdbff5877
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227286
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#34999}

modules/video_coding/h264_packet_buffer.h

@@ -0,0 +1,56 @@
+/*
+ *  Copyright (c) 2021 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.
+ */
+
+#ifndef MODULES_VIDEO_CODING_H264_PACKET_BUFFER_H_
+#define MODULES_VIDEO_CODING_H264_PACKET_BUFFER_H_
+
+#include <array>
+#include <memory>
+#include <vector>
+
+#include "absl/base/attributes.h"
+#include "absl/types/optional.h"
+#include "modules/video_coding/packet_buffer.h"
+#include "rtc_base/numerics/sequence_number_util.h"
+
+namespace webrtc {
+
+class H264PacketBuffer {
+ public:
+  // The H264PacketBuffer does the same job as the PacketBuffer but for H264
+  // only. To make it fit in with surronding code the PacketBuffer input/output
+  // classes are used.
+  using Packet = video_coding::PacketBuffer::Packet;
+  using InsertResult = video_coding::PacketBuffer::InsertResult;
+
+  explicit H264PacketBuffer(bool idr_only_keyframes_allowed);
+
+  ABSL_MUST_USE_RESULT InsertResult
+  InsertPacket(std::unique_ptr<Packet> packet);
+
+ private:
+  static constexpr int kBufferSize = 2048;
+
+  std::unique_ptr<Packet>& GetPacket(int64_t unwrapped_seq_num);
+  bool BeginningOfStream(const Packet& packet) const;
+  std::vector<std::unique_ptr<Packet>> FindFrames(int64_t unwrapped_seq_num);
+  bool MaybeAssembleFrame(int64_t start_seq_num_unwrapped,
+                          int64_t end_sequence_number_unwrapped,
+                          std::vector<std::unique_ptr<Packet>>& packets);
+
+  const bool idr_only_keyframes_allowed_;
+  std::array<std::unique_ptr<Packet>, kBufferSize> buffer_;
+  absl::optional<int64_t> last_continuous_unwrapped_seq_num_;
+  SeqNumUnwrapper<uint16_t> seq_num_unwrapper_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_H264_PACKET_BUFFER_H_