Remove WebRTC-VP8ConferenceTemporalLayers field trial

WebRTC-VP8ConferenceTemporalLayers experiment is restricted to <= M126. Number of temporal layers is controlled via scalaiblity mode now.

Bug: webrtc:351644568, b/352504711,  chromium:40097057, b/140159553
Change-Id: I025f8f64e8d5144cf54fe8bf26e8b99daae6e079
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/357104
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42637}

experiments/field_trials.py

@@ -805,9 +805,6 @@ POLICY_EXEMPT_FIELD_TRIALS: FrozenSet[FieldTrial] = frozenset([
     FieldTrial('WebRTC-VP8-Postproc-Config-Arm',
                42231704,
                INDEFINITE),
-    FieldTrial('WebRTC-VP8ConferenceTemporalLayers',
-               42234443,
-               INDEFINITE),
     FieldTrial('WebRTC-VP8IosMaxNumberOfThread',
                42220027,
                date(2024, 4, 1)),
@@ -887,7 +884,7 @@ POLICY_EXEMPT_FIELD_TRIALS: FrozenSet[FieldTrial] = frozenset([
 ])  # yapf: disable
 
 POLICY_EXEMPT_FIELD_TRIALS_DIGEST: str = \
-    'd6beac9eb318c70cd1695598b3d3c069cd17b42f'
+    'ad853beba9dddb16d9f45164a8d69b5d01e7d1c9'
 
 REGISTERED_FIELD_TRIALS: FrozenSet[FieldTrial] = ACTIVE_FIELD_TRIALS.union(
     POLICY_EXEMPT_FIELD_TRIALS)

test/BUILD.gn

@@ -1391,6 +1391,8 @@ rtc_library("video_codec_tester") {
     "../rtc_base:timeutils",
     "../rtc_base/synchronization:mutex",
     "../system_wrappers",
+    "../system_wrappers:field_trial",
+    "../test:explicit_key_value_config",
     "../test:fileutils",
     "../video/config:streams_config",
     "//third_party/abseil-cpp/absl/strings",

test/video_codec_tester.cc

@@ -46,7 +46,9 @@
 #include "rtc_base/synchronization/mutex.h"
 #include "rtc_base/task_queue_for_test.h"
 #include "rtc_base/time_utils.h"
+#include "system_wrappers/include/field_trial.h"
 #include "system_wrappers/include/sleep.h"
+#include "test/explicit_key_value_config.h"
 #include "test/scoped_key_value_config.h"
 #include "test/testsupport/file_utils.h"
 #include "test/testsupport/frame_reader.h"
@@ -1291,11 +1293,7 @@ void ConfigureSimulcast(VideoCodec* vc) {
     return;
   }
 
-  ScopedKeyValueConfig field_trials((rtc::StringBuilder()
+  ExplicitKeyValueConfig field_trials(field_trial::GetFieldTrialString());
-                                     << "WebRTC-VP8ConferenceTemporalLayers/"
-                                     << num_temporal_layers << "/")
-                                        .str());
-
   const std::vector<webrtc::VideoStream> streams = cricket::GetSimulcastConfig(
       /*min_layer=*/1, num_spatial_layers, vc->width, vc->height,
       /*is_screenshare=*/false, /*temporal_layers_supported=*/true,
@@ -1312,8 +1310,7 @@ void ConfigureSimulcast(VideoCodec* vc) {
     SimulcastStream* ss = &vc->simulcastStream[i];
     ss->width = streams[i].width;
     ss->height = streams[i].height;
-    RTC_CHECK_EQ(*streams[i].num_temporal_layers, num_temporal_layers);
+    ss->numberOfTemporalLayers = num_temporal_layers;
-    ss->numberOfTemporalLayers = *streams[i].num_temporal_layers;
     ss->maxBitrate = streams[i].max_bitrate_bps / 1000;
     ss->targetBitrate = streams[i].target_bitrate_bps / 1000;
     ss->minBitrate = streams[i].min_bitrate_bps / 1000;

video/config/simulcast.cc

@@ -178,27 +178,6 @@ std::vector<SimulcastFormat> GetSimulcastFormats(
   return formats;
 }
 
-// Multiway: Number of temporal layers for each simulcast stream.
-int DefaultNumberOfTemporalLayers(const webrtc::FieldTrialsView& trials) {
-  const std::string group_name =
-      trials.Lookup("WebRTC-VP8ConferenceTemporalLayers");
-  if (group_name.empty())
-    return kDefaultNumTemporalLayers;
-
-  int num_temporal_layers = kDefaultNumTemporalLayers;
-  if (sscanf(group_name.c_str(), "%d", &num_temporal_layers) == 1 &&
-      num_temporal_layers > 0 &&
-      num_temporal_layers <= webrtc::kMaxTemporalStreams) {
-    return num_temporal_layers;
-  }
-
-  RTC_LOG(LS_WARNING) << "Attempt to set number of temporal layers to "
-                         "incorrect value: "
-                      << group_name;
-
-  return kDefaultNumTemporalLayers;
-}
-
 int FindSimulcastFormatIndex(int width,
                              int height,
                              bool enable_lowres_bitrate_interpolation,
@@ -260,7 +239,8 @@ std::vector<webrtc::VideoStream> GetNormalSimulcastLayers(
   std::vector<webrtc::VideoStream> layers(layer_count);
   const bool enable_lowres_bitrate_interpolation =
       EnableLowresBitrateInterpolation(trials);
-  const int num_temporal_layers = DefaultNumberOfTemporalLayers(trials);
+  const int num_temporal_layers =
+      temporal_layers_supported ? kDefaultNumTemporalLayers : 1;
   // Format width and height has to be divisible by |2 ^ num_simulcast_layers -
   // 1|.
   width = NormalizeSimulcastSize(trials, width, layer_count);
@@ -270,8 +250,7 @@ std::vector<webrtc::VideoStream> GetNormalSimulcastLayers(
   for (size_t s = layer_count - 1;; --s) {
     layers[s].width = width;
     layers[s].height = height;
-    layers[s].num_temporal_layers =
+    layers[s].num_temporal_layers = num_temporal_layers;
-        temporal_layers_supported ? num_temporal_layers : 1;
 
     SimulcastFormat interpolated_format = InterpolateSimulcastFormat(
         width, height, /*max_roundup_rate=*/absl::nullopt,