Make sure temporal layered screenshare frames are sent in at least 2s.

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

Index: webrtc/modules/video_coding/codecs/vp8/screenshare_layers.cc
diff --git a/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.cc b/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.cc
index 2b7f7195d54bcf822606ce93848e07ba207095c5..aa75ef1414d92549f4b664a81da870277b11abd5 100644
--- a/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.cc
@@ -47,6 +47,10 @@ const int ScreenshareLayers::kTl1SyncFlags =
     VP8_EFLAG_NO_REF_ARF | VP8_EFLAG_NO_REF_GF | VP8_EFLAG_NO_UPD_ARF |
     VP8_EFLAG_NO_UPD_LAST;
 
+// Always emit a frame with certain interval, even if bitrate targets have
+// been exceeded.
+const int ScreenshareLayers::kMaxFrameIntervalMs = 2000;
+
 ScreenshareLayers::ScreenshareLayers(int num_temporal_layers,
                                      uint8_t initial_tl0_pic_idx,
                                      Clock* clock)
@@ -85,11 +89,12 @@ int ScreenshareLayers::EncodeFlags(uint32_t timestamp) {
 
   int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
   int flags = 0;
-
   if (active_layer_ == -1 ||
       layers_[active_layer_].state != TemporalLayer::State::kDropped) {
+    layers_[0].CheckFrameInterval(unwrapped_timestamp);
     if (layers_[0].debt_bytes_ > max_debt_bytes_) {
       // Must drop TL0, encode TL1 instead.
+      layers_[1].CheckFrameInterval(unwrapped_timestamp);

[stefan-webrtc, 2016/04/07 12:53:12]

Do we want the same behavior in TL1, or should we only enforce 0.5 fps in TL0? I
think TL0 would be enough?

[sprang_webrtc, 2016/04/07 13:03:32]

Yeah, I think only doing it for TL0 makes sense.

       if (layers_[1].debt_bytes_ > max_debt_bytes_) {
         // Must drop both TL0 and TL1.
         active_layer_ = -1;
@@ -104,6 +109,7 @@ int ScreenshareLayers::EncodeFlags(uint32_t timestamp) {
   switch (active_layer_) {
     case 0:
       flags = kTl0Flags;
+      layers_[0].last_emitted_timsetamp_ = unwrapped_timestamp;

[stefan-webrtc, 2016/04/07 12:53:12]

last_emitted_timestamp

[sprang_webrtc, 2016/04/07 13:03:32]

Done.

       break;
     case 1:
       if (TimeToSync(unwrapped_timestamp)) {
@@ -112,6 +118,7 @@ int ScreenshareLayers::EncodeFlags(uint32_t timestamp) {
       } else {
         flags = kTl1Flags;
       }
+      layers_[1].last_emitted_timsetamp_ = unwrapped_timestamp;
       break;
     case -1:
       flags = -1;
@@ -122,14 +129,13 @@ int ScreenshareLayers::EncodeFlags(uint32_t timestamp) {
       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 {
     ts_diff = unwrapped_timestamp - last_timestamp_;
   }
-
+  // Make sure both frame droppers leak out bits.
   layers_[0].UpdateDebt(ts_diff / 90);
   layers_[1].UpdateDebt(ts_diff / 90);
   last_timestamp_ = timestamp;
@@ -302,6 +308,14 @@ void ScreenshareLayers::TemporalLayer::UpdateDebt(int64_t delta_ms) {
   }
 }
 
+void ScreenshareLayers::TemporalLayer::CheckFrameInterval(int64_t timestamp) {
+  if (last_emitted_timsetamp_ != -1 &&
+      (timestamp - last_emitted_timsetamp_) / 90 > kMaxFrameIntervalMs) {
+    // Too long time has passed since the last frame was emitted, cancel debt.
+    debt_bytes_ = 0;
+  }
+}
+
 void ScreenshareLayers::UpdateHistograms() {
   if (stats_.first_frame_time_ms_ == -1)
     return;