Implement the NackModule as part of the new jitter buffer.

webrtc/modules/video_coding/nack_module.h

+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_VIDEO_CODING_NACK_MODULE_H_
+#define WEBRTC_MODULES_VIDEO_CODING_NACK_MODULE_H_
+
+#include <map>
+#include <vector>
+#include <set>
+
+#include "webrtc/base/thread_annotations.h"
+#include "webrtc/modules/include/module.h"
+#include "webrtc/modules/video_coding/include/video_coding_defines.h"
+#include "webrtc/modules/video_coding/packet.h"
+#include "webrtc/system_wrappers/include/clock.h"
+#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
+
+namespace webrtc {
+
+class NackModule : public Module {
+ public:

[stefan-webrtc, 2016/02/26 09:26:55]

I think we need a method which can be used to inform the nack module that the
stream is decodable beyond a certain timestamp (or sequence number, maybe), so
that the nack module can drop all nacks prior to that timestamp. Otherwise it
may keep nacking things that won't be used.

[philipel, 2016/02/26 15:12:07]

Agree, implemented.

+  NackModule(Clock* clock,
+             VCMNackSender* nack_sender,
+             VCMKeyFrameRequestSender* keyframe_request_sender);
+
+  void OnReceivedPacket(const VCMPacket& packet);
+  void UpdateRtt(int64_t rtt_ms);
+  void Stop();
+
+  // Module implementation
+  int64_t TimeUntilNextProcess() override;
+  int32_t Process() override;
+
+ private:
+  static const uint16_t kMaxNackPackets = 1000;
+  static const uint16_t kMaxReorderedPackets = 128;
+  static const uint16_t kNumReorderingBuckets = 5;
+  static const uint16_t kDefaultRttMs = 100;
+  static const uint8_t kMaxNackRetries = 10;
+  static const uint8_t kProcessFrequency = 50;
+  static const uint8_t kProcessIntervalMs = 1000 / kProcessFrequency;
+
+  // This class holds the sequence number of the packet that is in the nack list
+  // as well as the meta data about when it should be nacked and how many times
+  // we have tried to nack this packet.
+  struct NackInfo {
+    NackInfo();
+    NackInfo(uint16_t seq_num, uint16_t send_at_seq_num);
+
+    uint16_t seq_num;
+    uint16_t send_at_seq_num;
+    int64_t send_at_time;

[stefan-webrtc, 2016/02/26 09:26:55]

Would it be more logical to have "sent_at_time" and sent_at_seq_num? That way
the time to resend the packet can be dynamic, which is good since the rtt may
vary.

[philipel, 2016/02/26 15:12:07]

For the timestamp I think this is a good idea.

+    int retries;
+  };
+
+  void AddPacketsToNack(uint16_t seq_num_start, uint16_t seq_num_end)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
+  // Removes packets from the nack list until the next
+  // keyframe. Returns true if packets were removed.
+  bool RemovePacketsUntilKeyframe()
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+  void RemovePacketFromNack(uint16_t seq_num)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
+  // Which fields to consider when deciding
+  // which packet to nack in GetNackBatch.
+  enum NackFilterOptions {kSeqNumOnly,
+                          kTimeOnly,
+                          kSeqNumAndTime};

[stefan-webrtc, 2016/02/26 09:26:55]

Place type definitions directly after "private:"

[philipel, 2016/02/26 15:12:07]

Done.

+  std::vector<uint16_t> GetNackBatch(NackFilterOptions options)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
+  // Update the reordering distribution.
+  void UpdateReorderingStatistics(uint16_t seq_num)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
+  // Returns how many packets we have to wait in order to receive
+  // the packet with probability |probabilty| or higher.
+  int WaitNumberOfPackets(float probability) const
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
+  rtc::CriticalSection crit_;
+  Clock* const clock_;
+  VCMNackSender* const nack_sender_;
+  VCMKeyFrameRequestSender* const keyframe_request_sender_;
+
+  SequenceNumberUnwrapper unwrapper_;
+  std::map<int64_t, NackInfo> nack_list_ GUARDED_BY(crit_);
+  std::set<int64_t> seq_num_keyframes_ GUARDED_BY(crit_);

[stefan-webrtc, 2016/02/26 09:26:55]

std::set<uint16_t>, right?

[philipel, 2016/02/26 15:12:07]

I use the unrolled sequence number as the key, maybe rename it to
unwrapped_keyframes_?

+  bool running_ GUARDED_BY(crit_);
+  bool initialized_ GUARDED_BY(crit_);
+  int64_t rtt_ms_ GUARDED_BY(crit_);
+  uint16_t last_seq_num_ GUARDED_BY(crit_);
+  int64_t last_process_time_ms_ GUARDED_BY(crit_);
+
+  uint8_t reordering_index_ GUARDED_BY(crit_);
+  uint8_t reordering_count_ GUARDED_BY(crit_);

[stefan-webrtc, 2016/02/26 09:26:55]

int

[philipel, 2016/02/26 15:12:07]

Done.

+  int8_t reordering_occurences_[kMaxReorderedPackets] GUARDED_BY(crit_);

[stefan-webrtc, 2016/02/26 09:26:55]

int

[philipel, 2016/02/26 15:12:07]

Done.

+  uint8_t reordering_buckets_[kNumReorderingBuckets] GUARDED_BY(crit_);

[stefan-webrtc, 2016/02/26 09:26:55]

int

[philipel, 2016/02/26 15:12:07]

Done.

+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_VIDEO_CODING_NACK_MODULE_H_