In screenshare mode, suppress VP8 bitrate overshoot and increase quality

webrtc/modules/video_coding/codecs/vp8/screenshare_layers.cc

 /* Copyright (c) 2013 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.
 */
 
 #include "webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h"
 
 #include <stdlib.h>
 
+#include "webrtc/base/checks.h"
 #include "vpx/vpx_encoder.h"
 #include "vpx/vp8cx.h"
 #include "webrtc/modules/video_coding/codecs/interface/video_codec_interface.h"
 
 namespace webrtc {
 
-enum { kOneSecond90Khz = 90000 };
+static const int kOneSecond90Khz = 90000;
+static const int kMinTimeBetweenSyncs = kOneSecond90Khz * 5;
+static const int kMaxTimeBetweenSyncs = kOneSecond90Khz * 10;
+static const int kQpDeltaThresholdForSync = 8;
 
 const double ScreenshareLayers::kMaxTL0FpsReduction = 2.5;
 const double ScreenshareLayers::kAcceptableTargetOvershoot = 2.0;
 
+// Since this is TL0 we only allow updating and predicting from the LAST
+// reference frame.
+const int ScreenshareLayers::kTl0Flags =
+    VP8_EFLAG_NO_UPD_GF | VP8_EFLAG_NO_UPD_ARF | VP8_EFLAG_NO_REF_GF |
+    VP8_EFLAG_NO_REF_ARF;
+
+// Allow predicting from both TL0 and TL1.
+const int ScreenshareLayers::kTl1Flags =
+    VP8_EFLAG_NO_REF_ARF | VP8_EFLAG_NO_UPD_ARF | VP8_EFLAG_NO_UPD_LAST;
+
+// Allow predicting from only TL0 to allow participants to switch to the high
+// bitrate stream. This means predicting only from the LAST reference frame, but
+// only updating GF to not corrupt TL0.
+const int ScreenshareLayers::kTl1SyncFlags =
+    VP8_EFLAG_NO_REF_ARF | VP8_EFLAG_NO_REF_GF | VP8_EFLAG_NO_UPD_ARF |
+    VP8_EFLAG_NO_UPD_LAST;
+
 ScreenshareLayers::ScreenshareLayers(int num_temporal_layers,
-                                     uint8_t initial_tl0_pic_idx,
-                                     FrameDropper* tl0_frame_dropper,
-                                     FrameDropper* tl1_frame_dropper)
-    : tl0_frame_dropper_(tl0_frame_dropper),
-      tl1_frame_dropper_(tl1_frame_dropper),
-      number_of_temporal_layers_(num_temporal_layers),
+                                     uint8_t initial_tl0_pic_idx)
+    : number_of_temporal_layers_(num_temporal_layers),
       last_base_layer_sync_(false),
       tl0_pic_idx_(initial_tl0_pic_idx),
-      active_layer_(0),
-      framerate_(5),
-      last_sync_timestamp_(-1) {
+      active_layer_(-1),
+      last_timestamp_(-1),
+      last_sync_timestamp_(-1),
+      min_qp_(-1),
+      max_qp_(-1),
+      max_debt_bytes_(0),
+      frame_rate_(-1) {
   assert(num_temporal_layers > 0);
   assert(num_temporal_layers <= 2);
-  assert(tl0_frame_dropper && tl1_frame_dropper);
 }
 
 int ScreenshareLayers::CurrentLayerId() const {
   // Codec does not use temporal layers for screenshare.
   return 0;
 }
 
 int ScreenshareLayers::EncodeFlags(uint32_t timestamp) {
   if (number_of_temporal_layers_ <= 1) {
     // No flags needed for 1 layer screenshare.
     return 0;
   }
-  CalculateFramerate(timestamp);
+
+  int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
   int flags = 0;
-  // Note that ARF on purpose isn't used in this scheme since it is allocated
-  // for the last key frame to make key frame caching possible.
-  if (tl0_frame_dropper_->DropFrame()) {
-    // Must drop TL0, encode TL1 instead.
-    if (tl1_frame_dropper_->DropFrame()) {
-      // Must drop both TL0 and TL1.
+
+  if (active_layer_ == -1 ||
+      layers_[active_layer_].state != TemporalLayer::State::kDropped) {
+    if (layers_[0].debt_bytes_ > max_debt_bytes_) {
+      // Must drop TL0, encode TL1 instead.
+      if (layers_[1].debt_bytes_ > max_debt_bytes_) {
+        // Must drop both TL0 and TL1.
+        active_layer_ = -1;
+      } else {
+        active_layer_ = 1;
+      }
+    } else {
+      active_layer_ = 0;
+    }
+  }
+
+  switch (active_layer_) {
+    case 0:
+      flags = kTl0Flags;
+      break;
+    case 1:
+      if (TimeToSync(unwrapped_timestamp)) {
+        last_sync_timestamp_ = unwrapped_timestamp;
+        flags = kTl1SyncFlags;
+      } else {
+        flags = kTl1Flags;
+      }
+      break;
+    case -1:
       flags = -1;
-    } else {
-      active_layer_ = 1;
-      if (TimeToSync(timestamp)) {
-        last_sync_timestamp_ = timestamp;
-        // Allow predicting from only TL0 to allow participants to switch to the
-        // high bitrate stream. This means predicting only from the LAST
-        // reference frame, but only updating GF to not corrupt TL0.
-        flags = VP8_EFLAG_NO_REF_ARF;
-        flags |= VP8_EFLAG_NO_REF_GF;
-        flags |= VP8_EFLAG_NO_UPD_ARF;
-        flags |= VP8_EFLAG_NO_UPD_LAST;
-      } else {
-        // Allow predicting from both TL0 and TL1.
-        flags = VP8_EFLAG_NO_REF_ARF;
-        flags |= VP8_EFLAG_NO_UPD_ARF;
-        flags |= VP8_EFLAG_NO_UPD_LAST;
-      }
-    }
+      break;
+    default:
+      flags = -1;
+      RTC_NOTREACHED();
+  }
+
+  // Make sure both frame droppers leak out bits.
+  int64_t ts_diff;
+  if (last_timestamp_ == -1) {
+    ts_diff = kOneSecond90Khz / (frame_rate_ <= 0 ? 5 : frame_rate_);
   } else {
-    active_layer_ = 0;
-    // Since this is TL0 we only allow updating and predicting from the LAST
-    // reference frame.
-    flags = VP8_EFLAG_NO_UPD_GF;
-    flags |= VP8_EFLAG_NO_UPD_ARF;
-    flags |= VP8_EFLAG_NO_REF_GF;
-    flags |= VP8_EFLAG_NO_REF_ARF;
+    ts_diff = unwrapped_timestamp - last_timestamp_;
   }
-  // Make sure both frame droppers leak out bits.
-  tl0_frame_dropper_->Leak(framerate_);
-  tl1_frame_dropper_->Leak(framerate_);
+
+  layers_[0].UpdateDebt(ts_diff / 90);
+  layers_[1].UpdateDebt(ts_diff / 90);
+  last_timestamp_ = timestamp;
   return flags;
 }
 
-bool ScreenshareLayers::ConfigureBitrates(int bitrate_kbit,
-                                          int max_bitrate_kbit,
+bool ScreenshareLayers::ConfigureBitrates(int bitrate_kbps,
+                                          int max_bitrate_kbps,
                                           int framerate,
                                           vpx_codec_enc_cfg_t* cfg) {
-  if (framerate > 0)
-    framerate_ = framerate;
+  layers_[0].target_rate_kbps_ = bitrate_kbps;
+  layers_[1].target_rate_kbps_ = max_bitrate_kbps;
 
-  tl0_frame_dropper_->SetRates(bitrate_kbit, framerate_);
-  tl1_frame_dropper_->SetRates(max_bitrate_kbit, framerate_);
+  int target_bitrate_kbps = bitrate_kbps;
 
   if (cfg != nullptr) {
     // Calculate a codec target bitrate. This may be higher than TL0, gaining
     // quality at the expense of frame rate at TL0. Constraints:
     // - TL0 frame rate should not be less than framerate / kMaxTL0FpsReduction.
     // - Target rate * kAcceptableTargetOvershoot should not exceed TL1 rate.
-    double target_bitrate =
-        std::min(bitrate_kbit * kMaxTL0FpsReduction,
-                 max_bitrate_kbit / kAcceptableTargetOvershoot);
-    cfg->rc_target_bitrate =
-        std::max(static_cast<unsigned int>(bitrate_kbit),
-                 static_cast<unsigned int>(target_bitrate + 0.5));
+    target_bitrate_kbps =
+        std::min(bitrate_kbps * kMaxTL0FpsReduction,
+                 max_bitrate_kbps / kAcceptableTargetOvershoot);
+
+    // Don't reconfigure qp limits during quality boost frames.
+    if (layers_[active_layer_].state != TemporalLayer::State::kQualityBoost) {
+      min_qp_ = cfg->rc_min_quantizer;
+      max_qp_ = cfg->rc_max_quantizer;
+      // After a dropped frame, a frame with max qp will be encoded and the
+      // quality will then ramp up from there. To boost the speed of recovery,
+      // encode the next frame with lower max qp. TL0 is the most important to
+      // improve since the errors in this layer will propagate to TL1.
+      // Currently, reduce max qp by 20% for TL0 and 15% for TL1.
+      layers_[0].enhanced_max_qp = min_qp_ + (((max_qp_ - min_qp_) * 80) / 100);
+      layers_[1].enhanced_max_qp = min_qp_ + (((max_qp_ - min_qp_) * 85) / 100);
+    }
+
+    cfg->rc_target_bitrate = std::max(bitrate_kbps, target_bitrate_kbps);
   }
 
+  int avg_frame_size = (target_bitrate_kbps * 1000) / (8 * framerate);
+  max_debt_bytes_ = 4 * avg_frame_size;
+
   return true;
 }
 
-void ScreenshareLayers::FrameEncoded(unsigned int size, uint32_t timestamp) {
+void ScreenshareLayers::FrameEncoded(unsigned int size,
+                                     uint32_t timestamp,
+                                     int qp) {
+  if (size == 0) {
+    layers_[active_layer_].state = TemporalLayer::State::kDropped;
+    return;
+  }
+  if (layers_[active_layer_].state == TemporalLayer::State::kDropped) {
+    layers_[active_layer_].state = TemporalLayer::State::kQualityBoost;
+  }
+
+  if (qp != -1)
+    layers_[active_layer_].last_qp = qp;
+
   if (active_layer_ == 0) {
-    tl0_frame_dropper_->Fill(size, true);
+    layers_[0].debt_bytes_ += size;
+    layers_[1].debt_bytes_ += size;
+  } else if (active_layer_ == 1) {
+    layers_[1].debt_bytes_ += size;
   }
-  tl1_frame_dropper_->Fill(size, true);
 }
 
 void ScreenshareLayers::PopulateCodecSpecific(bool base_layer_sync,
                                               CodecSpecificInfoVP8 *vp8_info,
                                               uint32_t timestamp) {
+  int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
   if (number_of_temporal_layers_ == 1) {
     vp8_info->temporalIdx = kNoTemporalIdx;
     vp8_info->layerSync = false;
     vp8_info->tl0PicIdx = kNoTl0PicIdx;
   } else {
     vp8_info->temporalIdx = active_layer_;
     if (base_layer_sync) {
       vp8_info->temporalIdx = 0;
-      last_sync_timestamp_ = timestamp;
+      last_sync_timestamp_ = unwrapped_timestamp;
     } else if (last_base_layer_sync_ && vp8_info->temporalIdx != 0) {
       // Regardless of pattern the frame after a base layer sync will always
       // be a layer sync.
-      last_sync_timestamp_ = timestamp;
+      last_sync_timestamp_ = unwrapped_timestamp;
     }
-    vp8_info->layerSync = (last_sync_timestamp_ == timestamp);
+    vp8_info->layerSync = last_sync_timestamp_ != -1 &&
+                          last_sync_timestamp_ == unwrapped_timestamp;
     if (vp8_info->temporalIdx == 0) {
       tl0_pic_idx_++;
     }
     last_base_layer_sync_ = base_layer_sync;
     vp8_info->tl0PicIdx = tl0_pic_idx_;
   }
 }
 
-bool ScreenshareLayers::TimeToSync(uint32_t timestamp) const {
-  const uint32_t timestamp_diff = timestamp - last_sync_timestamp_;
-  return last_sync_timestamp_ < 0 || timestamp_diff > kOneSecond90Khz;
+bool ScreenshareLayers::TimeToSync(int64_t timestamp) const {
+  if (active_layer_ != 1) {
+    RTC_NOTREACHED();
+    return false;
+  }
+  DCHECK_NE(-1, layers_[0].last_qp);
+  if (layers_[1].last_qp == -1) {
+    // First frame in TL1 should only depend on TL0 since there are no
+    // previous frames in TL1.
+    return true;
+  }
+
+  DCHECK_NE(-1, last_sync_timestamp_);
+  int64_t timestamp_diff = timestamp - last_sync_timestamp_;
+  if (timestamp_diff > kMaxTimeBetweenSyncs) {
+    // After a certain time, force a sync frame.
+    return true;
+  } else if (timestamp_diff < kMinTimeBetweenSyncs) {
+    // If too soon from previous sync frame, don't issue a new one.
+    return false;
+  }
+  // Issue a sync frame if difference in quality between TL0 and TL1 isn't too
+  // large.
+  if (layers_[0].last_qp - layers_[1].last_qp < kQpDeltaThresholdForSync)
+    return true;
+  return false;
 }
 
-void ScreenshareLayers::CalculateFramerate(uint32_t timestamp) {
-  timestamp_list_.push_front(timestamp);
-  // Remove timestamps older than 1 second from the list.
-  uint32_t timestamp_diff = timestamp - timestamp_list_.back();
-  while (timestamp_diff > kOneSecond90Khz) {
-    timestamp_list_.pop_back();
-    timestamp_diff = timestamp - timestamp_list_.back();
+bool ScreenshareLayers::UpdateConfiguration(vpx_codec_enc_cfg_t* cfg) {
+  if (max_qp_ == -1)
+    return false;
+
+  // If layer is in the quality boost state (following a dropped frame), update
+  // the configuration with the adjusted (lower) qp and set the state back to
+  // normal.
+  unsigned int adjusted_max_qp;
+  if (layers_[active_layer_].state == TemporalLayer::State::kQualityBoost &&
+      layers_[active_layer_].enhanced_max_qp != -1) {
+    adjusted_max_qp = layers_[active_layer_].enhanced_max_qp;
+    layers_[active_layer_].state = TemporalLayer::State::kNormal;
+  } else {
+    if (max_qp_ == -1)
+      return false;
+    adjusted_max_qp = max_qp_;  // Set the normal max qp.
   }
-  // If we have encoded frames within the last second, that number of frames
-  // is a reasonable first estimate of the framerate.
-  framerate_ = timestamp_list_.size();
-  if (timestamp_diff > 0) {
-    // Estimate the framerate by dividing the number of timestamp diffs with
-    // the sum of the timestamp diffs (with rounding).
-    framerate_ = (kOneSecond90Khz * (timestamp_list_.size() - 1) +
-        timestamp_diff / 2) / timestamp_diff;
+
+  if (adjusted_max_qp == cfg->rc_max_quantizer)
+    return false;
+
+  cfg->rc_max_quantizer = adjusted_max_qp;
+  return true;
+}
+
+void ScreenshareLayers::TemporalLayer::UpdateDebt(int64_t delta_ms) {
+  uint32_t debt_reduction_bytes = target_rate_kbps_ * delta_ms / 8;
+  if (debt_reduction_bytes >= debt_bytes_) {
+    debt_bytes_ = 0;
+  } else {
+    debt_bytes_ -= debt_reduction_bytes;
   }
 }
 
 }  // namespace webrtc