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Ship ability to opt-in to VP9/AV1 simulcast (re-land).

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This makes "WebRTC-AllowDisablingLegacyScalability" enabled-by-default,
meaning any app can opt-in to spec-compliant simulcast when
scalabilityMode is specified.

The opt-in criteria is also made more restricitve: you now have to
specify both scalabilityMode and scaleResolutionDownBy to get simulcast,
otherwise you continue to get legacy "single stream" path.

The reason for this is not to cause any surprises in use cases like
[{scalabilityMode:"L1T1", active:true}, {active:false}, {active:false}]
In cases like this where scaleResolutionDownBy is not specified, it
defaults to 4:2:1 if simulcast is used but the legacy path caps it to
one stream, meaning full resolution. By restricing simulcast only to
cases that set scaleResolutionDownBy, we remove the risk of an app
getting a different resolution than expected due to opt-in.

Bug: webrtc:14884, webrtc:15005
Change-Id: I5efb87af60afaeb1e3ff76698d887aaa1f9d63a9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/298922
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39660}
This commit is contained in:
Henrik Boström 2023-03-23 17:03:43 +01:00 committed by WebRTC LUCI CQ
parent dfc84087e3
commit adb946054c
2 changed files with 31 additions and 29 deletions
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9
media/engine/webrtc_video_engine.cc
View File

@ -2507,12 +2507,13 @@ WebRtcVideoChannel::WebRtcVideoSendStream::CreateVideoEncoderConfig(
// `legacy_scalability_mode` and codec used.
encoder_config.number_of_streams = parameters_.config.rtp.ssrcs.size();
bool legacy_scalability_mode = true;
// TODO(https://crbug.com/webrtc/14884): When simulcast VP9 is ready to ship,
// don't require a field trial to set `legacy_scalability_mode` to false here.
if (call_->trials().IsEnabled("WebRTC-AllowDisablingLegacyScalability")) {
// TODO(https://crbug.com/webrtc/14884): This is only used as a kill-switch
// in case of serious bugs - when this reaches Stable, delete the field trial.
if (!call_->trials().IsDisabled("WebRTC-AllowDisablingLegacyScalability")) {
for (const webrtc::RtpEncodingParameters& encoding :
rtp_parameters_.encodings) {
if (encoding.scalability_mode.has_value()) {
if (encoding.scalability_mode.has_value() &&
encoding.scale_resolution_down_by.has_value()) {
legacy_scalability_mode = false;
break;
}

51
pc/peer_connection_simulcast_unittest.cc
View File

@ -1000,6 +1000,20 @@ class PeerConnectionSimulcastWithMediaFlowTests
return num_sending_layers == num_active_layers;
}
bool HasOutboundRtpWithRidAndScalabilityMode(
rtc::scoped_refptr<PeerConnectionTestWrapper> pc_wrapper,
absl::string_view rid,
absl::string_view expected_scalability_mode) {
rtc::scoped_refptr<const RTCStatsReport> report = GetStats(pc_wrapper);
std::vector<const RTCOutboundRtpStreamStats*> outbound_rtps =
report->GetStatsOfType<RTCOutboundRtpStreamStats>();
auto* outbound_rtp = FindOutboundRtpByRid(outbound_rtps, rid);
if (!outbound_rtp || !outbound_rtp->scalability_mode.is_defined()) {
return false;
}
return *outbound_rtp->scalability_mode == expected_scalability_mode;
}
bool OutboundRtpResolutionsAreLessThanOrEqualToExpectations(
rtc::scoped_refptr<PeerConnectionTestWrapper> pc_wrapper,
std::vector<RidAndResolution> resolutions) {
@ -1412,13 +1426,8 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
Optional(std::string("L3T3_KEY")));
}
// TODO(https://crbug.com/webrtc/14884): A field trial shouldn't be needed to
// get spec-compliant behavior!
TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
SendingThreeEncodings_VP9_Simulcast) {
test::ScopedFieldTrials field_trials(
"WebRTC-AllowDisablingLegacyScalability/Enabled/");
rtc::scoped_refptr<PeerConnectionTestWrapper> local_pc_wrapper = CreatePc();
rtc::scoped_refptr<PeerConnectionTestWrapper> remote_pc_wrapper = CreatePc();
ExchangeIceCandidates(local_pc_wrapper, remote_pc_wrapper);
@ -1433,13 +1442,16 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
transceiver->SetCodecPreferences(codecs);
// Opt-in to spec-compliant simulcast by explicitly setting the
// `scalability_mode`.
// `scalability_mode` and `scale_resolution_down_by` parameters.
rtc::scoped_refptr<RtpSenderInterface> sender = transceiver->sender();
RtpParameters parameters = sender->GetParameters();
ASSERT_EQ(parameters.encodings.size(), 3u);
parameters.encodings[0].scalability_mode = "L1T3";
parameters.encodings[0].scale_resolution_down_by = 4;
parameters.encodings[1].scalability_mode = "L1T3";
parameters.encodings[1].scale_resolution_down_by = 2;
parameters.encodings[2].scalability_mode = "L1T3";
parameters.encodings[2].scale_resolution_down_by = 1;
sender->SetParameters(parameters);
NegotiateWithSimulcastTweaks(local_pc_wrapper, remote_pc_wrapper, layers);
@ -1483,11 +1495,6 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
// changes from 1 (legacy SVC) to 3 (standard simulcast).
TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
SendingThreeEncodings_VP9_FromLegacyToSingleActiveWithScalability) {
// TODO(https://crbug.com/webrtc/14884): A field trial shouldn't be needed to
// get spec-compliant behavior!
test::ScopedFieldTrials field_trials(
"WebRTC-AllowDisablingLegacyScalability/Enabled/");
rtc::scoped_refptr<PeerConnectionTestWrapper> local_pc_wrapper = CreatePc();
rtc::scoped_refptr<PeerConnectionTestWrapper> remote_pc_wrapper = CreatePc();
ExchangeIceCandidates(local_pc_wrapper, remote_pc_wrapper);
@ -1515,6 +1522,7 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
ASSERT_EQ(parameters.encodings.size(), 3u);
parameters.encodings[0].active = true;
parameters.encodings[0].scalability_mode = "L2T2_KEY";
parameters.encodings[0].scale_resolution_down_by = 4.0;
parameters.encodings[1].active = false;
parameters.encodings[1].scalability_mode = absl::nullopt;
parameters.encodings[2].active = false;
@ -1525,14 +1533,10 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
// but only one is active.
EXPECT_TRUE_WAIT(HasOutboundRtpBytesSent(local_pc_wrapper, 3u, 1u),
kLongTimeoutForRampingUp.ms());
rtc::scoped_refptr<const RTCStatsReport> report = GetStats(local_pc_wrapper);
std::vector<const RTCOutboundRtpStreamStats*> outbound_rtps =
report->GetStatsOfType<RTCOutboundRtpStreamStats>();
ASSERT_THAT(outbound_rtps, SizeIs(3u));
auto* f_outbound_rtp = FindOutboundRtpByRid(outbound_rtps, "f");
ASSERT_TRUE(f_outbound_rtp);
ASSERT_TRUE(f_outbound_rtp->scalability_mode.is_defined());
EXPECT_THAT(*f_outbound_rtp->scalability_mode, StrEq("L2T2_KEY"));
// Reduce risk of flakiness by waiting until the scalability mode is reported.
EXPECT_TRUE_WAIT(HasOutboundRtpWithRidAndScalabilityMode(local_pc_wrapper,
"f", "L2T2_KEY"),
kLongTimeoutForRampingUp.ms());
// GetParameters() does not report any fallback.
parameters = sender->GetParameters();
@ -1543,14 +1547,8 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
EXPECT_FALSE(parameters.encodings[2].scalability_mode.has_value());
}
// TODO(https://crbug.com/webrtc/15005): A field trial shouldn't be needed to
// get spec-compliant behavior! The same field trial is also used for VP9
// simulcast (https://crbug.com/webrtc/14884).
TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
SendingThreeEncodings_AV1_Simulcast) {
test::ScopedFieldTrials field_trials(
"WebRTC-AllowDisablingLegacyScalability/Enabled/");
rtc::scoped_refptr<PeerConnectionTestWrapper> local_pc_wrapper = CreatePc();
// TODO(https://crbug.com/webrtc/15011): Expand testing support for AV1 or
// allow compile time checks so that gates like this isn't needed at runtime.
@ -1576,8 +1574,11 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
RtpParameters parameters = sender->GetParameters();
ASSERT_EQ(parameters.encodings.size(), 3u);
parameters.encodings[0].scalability_mode = "L1T3";
parameters.encodings[0].scale_resolution_down_by = 4;
parameters.encodings[1].scalability_mode = "L1T3";
parameters.encodings[1].scale_resolution_down_by = 2;
parameters.encodings[2].scalability_mode = "L1T3";
parameters.encodings[2].scale_resolution_down_by = 1;
sender->SetParameters(parameters);
NegotiateWithSimulcastTweaks(local_pc_wrapper, remote_pc_wrapper, layers);