Revert of Fix BitrateProber to match the requested bitrate more precisely

webrtc/modules/pacing/bitrate_prober.cc

Index: webrtc/modules/pacing/bitrate_prober.cc
diff --git a/webrtc/modules/pacing/bitrate_prober.cc b/webrtc/modules/pacing/bitrate_prober.cc
index d4007cc1ad5c7f0acd84c48cc4fd0fe8e2eae5f5..8e3c5e354795a17a6c9ed32c4e4e9b3343294186 100644
--- a/webrtc/modules/pacing/bitrate_prober.cc
+++ b/webrtc/modules/pacing/bitrate_prober.cc
@@ -20,6 +20,9 @@
 
 namespace {
 
+// Inactivity threshold above which probing is restarted.
+constexpr int kInactivityThresholdMs = 5000;
+
 // A minimum interval between probes to allow scheduling to be feasible.
 constexpr int kMinProbeDeltaMs = 1;
 
@@ -29,11 +32,18 @@
 // The minimum probing duration in ms.
 constexpr int kMinProbeDurationMs = 15;
 
+int ComputeDeltaFromBitrate(size_t probe_size, uint32_t bitrate_bps) {
+  RTC_CHECK_GT(bitrate_bps, 0);
+  // Compute the time delta needed to send probe_size bytes at bitrate_bps
+  // bps. Result is in milliseconds.
+  return static_cast<int>((1000ll * probe_size * 8) / bitrate_bps);
+}
 }  // namespace
 
 BitrateProber::BitrateProber()
     : probing_state_(ProbingState::kDisabled),
-      next_probe_time_ms_(-1),
+      probe_size_last_sent_(0),
+      time_last_probe_sent_ms_(-1),
       next_cluster_id_(0) {
   SetEnabled(true);
 }
@@ -60,8 +70,6 @@
   if (probing_state_ == ProbingState::kInactive &&
       !clusters_.empty() &&
       packet_size >= PacedSender::kMinProbePacketSize) {
-    // Send next probe right away.
-    next_probe_time_ms_ = -1;
     probing_state_ = ProbingState::kActive;
   }
 }
@@ -85,6 +93,9 @@
 }
 
 void BitrateProber::ResetState() {
+  time_last_probe_sent_ms_ = -1;
+  probe_size_last_sent_ = 0;
+
   // Recreate all probing clusters.
   std::queue<ProbeCluster> clusters;
   clusters.swap(clusters_);
@@ -101,19 +112,36 @@
   // Probing is not active or probing is already complete.
   if (probing_state_ != ProbingState::kActive || clusters_.empty())
     return -1;
-
+  // time_last_probe_sent_ms_ of -1 indicates no probes have yet been sent.
+  int64_t elapsed_time_ms;
+  if (time_last_probe_sent_ms_ == -1) {
+    elapsed_time_ms = 0;
+  } else {
+    elapsed_time_ms = now_ms - time_last_probe_sent_ms_;
+  }
+  // If no probes have been sent for a while, abort current probing and
+  // reset.
+  if (elapsed_time_ms > kInactivityThresholdMs) {
+    ResetState();
+    return -1;
+  }
+  // We will send the first probe packet immediately if no packet has been
+  // sent before.
   int time_until_probe_ms = 0;
-  if (next_probe_time_ms_ >= 0) {
-    time_until_probe_ms = next_probe_time_ms_ - now_ms;
-    // If we have waited more than 3 ms for a new packet we will restart probing
-    // again later.
+  if (probe_size_last_sent_ != 0 && probing_state_ == ProbingState::kActive) {
+    int next_delta_ms = ComputeDeltaFromBitrate(probe_size_last_sent_,
+                                                clusters_.front().bitrate_bps);
+    time_until_probe_ms = next_delta_ms - elapsed_time_ms;
+    // If we have waited more than 3 ms for a new packet to probe with we will
+    // consider this probing session over.
     const int kMaxProbeDelayMs = 3;
-    if (time_until_probe_ms < -kMaxProbeDelayMs) {
-      ResetState();
-      return -1;
+    if (next_delta_ms < kMinProbeDeltaMs ||
+        time_until_probe_ms < -kMaxProbeDelayMs) {
+      probing_state_ = ProbingState::kSuspended;
+      LOG(LS_INFO) << "Delta too small or missed probing accurately, suspend";
+      time_until_probe_ms = 0;
     }
   }
-
   return std::max(time_until_probe_ms, 0);
 }
 
@@ -134,16 +162,12 @@
 void BitrateProber::ProbeSent(int64_t now_ms, size_t bytes) {
   RTC_DCHECK(probing_state_ == ProbingState::kActive);
   RTC_DCHECK_GT(bytes, 0);
-
+  probe_size_last_sent_ = bytes;
+  time_last_probe_sent_ms_ = now_ms;
   if (!clusters_.empty()) {
     ProbeCluster* cluster = &clusters_.front();
-    if (cluster->sent_probes == 0) {
-      RTC_DCHECK_EQ(cluster->time_started_ms, -1);
-      cluster->time_started_ms = now_ms;
-    }
     cluster->sent_bytes += static_cast<int>(bytes);
     cluster->sent_probes += 1;
-    next_probe_time_ms_ = GetNextProbeTime(clusters_.front());
     if (cluster->sent_bytes >= cluster->min_bytes &&
         cluster->sent_probes >= cluster->min_probes) {
       clusters_.pop();
@@ -152,17 +176,4 @@
       probing_state_ = ProbingState::kSuspended;
   }
 }
-
-int64_t BitrateProber::GetNextProbeTime(const ProbeCluster& cluster) {
-  RTC_CHECK_GT(cluster.bitrate_bps, 0);
-  RTC_CHECK_GE(cluster.time_started_ms, 0);
-
-  // Compute the time delta from the cluster start to ensure probe bitrate stays
-  // close to the target bitrate. Result is in milliseconds.
-  int64_t delta_ms = (8000ll * cluster.sent_bytes + cluster.bitrate_bps / 2) /
-                  cluster.bitrate_bps;
-  return cluster.time_started_ms + delta_ms;
-}
-
-
 }  // namespace webrtc