Work on flexible mode and screen sharing.

webrtc/modules/video_coding/codecs/vp9/screenshare_layers.cc

+/* Copyright (c) 2015 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 <algorithm>
+#include "webrtc/modules/video_coding/codecs/vp9/screenshare_layers.h"
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+ScreenshareLayersVP9::ScreenshareLayersVP9(uint8_t num_layers)
+    : num_layers_(num_layers), current_layer_(0), last_ts_(0) {
+  RTC_DCHECK_GT(num_layers, 0);
+  RTC_DCHECK_LE(num_layers, kMaxVp9NumberOfSpatialLayers);
+  memset(bits_used_, 0, sizeof(bits_used_));
+  memset(threshold_kbps_, 0, sizeof(threshold_kbps_));
+}
+
+uint8_t ScreenshareLayersVP9::GetStartLayer() const {

[stefan-webrtc, 2015/10/28 13:59:04]

should this be called current_layer()? What is a start layer?

[philipel1, 2015/10/29 14:49:26]

The start layer is the first spatial layer to encode. I have added a comment in
the .h file.

+  return current_layer_;
+}
+
+void ScreenshareLayersVP9::ConfigureBitrate(int threshold_kbps,
+                                            uint8_t layer_id) {
+  // The upper layer can't have a max bitrate,
+  // and therefore it can't be set.

[stefan-webrtc, 2015/10/28 13:59:04]

Could you also explain why it can't have a max bitrate?

[philipel1, 2015/10/29 14:49:26]

I guess there is no reason other than that we would call codec_encode and it
would encode nothing.

+  RTC_DCHECK_LT(layer_id, num_layers_ - 1);
+  threshold_kbps_[layer_id] = threshold_kbps;
+}
+
+void ScreenshareLayersVP9::LayerFrameEncoded(unsigned int size_bytes,
+                                             uint8_t layer_id) {
+  RTC_DCHECK_LT(layer_id, num_layers_);
+  bits_used_[layer_id] += size_bytes * 8;
+}
+
+VP9EncoderImpl::SuperFrameRefSettings
+ScreenshareLayersVP9::GetSuperFrameSettings(uint32_t timestamp,
+                                            bool is_keyframe) {
+  VP9EncoderImpl::SuperFrameRefSettings settings;
+  if (last_ts_ == 0)

[stefan-webrtc, 2015/10/28 13:59:04]

0 isn't safe to use as "not initialized"

[philipel1, 2015/10/29 14:49:26]

Added a timestamp_initialized_ variable for initialization.

+    last_ts_ = timestamp;
+  float time_diff = (timestamp - last_ts_) / 90.f;

[stefan-webrtc, 2015/10/28 13:59:04]

I suspect that this won't handle the case where timestamp < last_ts_, for
instance when timestamp is 30 and last_ts_ 0xffffff. I think the subtraction
will be promoted to int and done with integers after which the result will be
converted to float for division. Should probably add a test to verify this.

[philipel1, 2015/10/29 14:49:26]

This will use unsigned arithmetics so it's working as inteded. I have added a
unittest for this case.

+  float total_bits_used = 0;

[stefan-webrtc, 2015/10/28 13:59:04]

I don't really think we need to count with fractions of bits, so int is probably
good enough for this class.

[philipel1, 2015/10/29 14:49:26]

I use floats not to count fractions of a bit, but to not loose fractions when
the difference in timestamps is divided by 90 :). If we were using an int
instead of float we could have a noticeable error in the calculation. For
example if we have 60 fps then the average frame tick diff is 90000/60 = 1500,
then we could have a rounding error of up to 89, which is 89/1500 = 0.0593, or
around 6% off the real time diff.

+  float total_threshold_kbps = 0;
+  current_layer_ = 0;
+
+  // Up to (num_layers - 1) because we only have
+  // (num_layers - 1) thresholds to check.
+  for (uint8_t layer_id = 0; layer_id < num_layers_ - 1; ++layer_id) {

[stefan-webrtc, 2015/10/28 13:59:04]

int

[philipel1, 2015/10/29 14:49:26]

Done.

+    bits_used_[layer_id] = std::max(
+        0.f, bits_used_[layer_id] - time_diff * threshold_kbps_[layer_id]);
+    total_bits_used += bits_used_[layer_id];
+    total_threshold_kbps += threshold_kbps_[layer_id];
+    if (!is_keyframe) {
+      settings.layer[layer_id].ref_buf1 = layer_id;

[stefan-webrtc, 2015/10/28 13:59:04]

Comment on what this code block does.

[philipel1, 2015/10/29 14:49:26]

Done.

+      if (total_bits_used > total_threshold_kbps * 1000)
+        current_layer_ = layer_id + 1;
+    }
+    settings.layer[layer_id].upd_buf = layer_id;
+  }
+  if (!is_keyframe)

[stefan-webrtc, 2015/10/28 13:59:04]

Comment on why !is_keyframe. Why not for key frames?

[philipel1, 2015/10/29 14:49:26]

Done.

+    settings.layer[num_layers_ - 1].ref_buf1 = num_layers_ - 1;
+  settings.layer[num_layers_ - 1].upd_buf = num_layers_ - 1;
+  settings.is_keyframe = is_keyframe;
+  settings.start_layer = current_layer_;
+  settings.stop_layer = num_layers_ - 1;
+  last_ts_ = timestamp;
+  return settings;
+}
+
+}  // namespace webrtc