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Ship ability to opt-in to VP9/AV1 simulcast.

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With this unflagging, an app can opt-in to simulcast when using multiple
encodings by specifying RTCRtpEncodingParameters.scalabilityMode. This
ensures backwards-compat with apps relying on 3 encodings to mean SVC
who traditionally have not specified scalabilityMode.

It fixes the spec/API bug of asking for simulcast and not getting
simulcast. The field trial exists only as a kill-switch with a TODO to
remove it.

This ships initial support, however note that the VP9/AV1 simulcast uses
SimulcastRateAllocator (just like VP8/H264 simulcast). This rate
allocator uses more kbps than SvcRateAllocator. This should be revisited
to avoid significant higher bitrates, for example when comparing VP9
simulcast to VP9 SVC.

Shipping the ability for apps to opt-in makes it easier to exercise
these new code paths and allows initial feedback from developers, but
due to the high bitrate (= same bitrate as VP8/H264 simulcast today)
many apps may find that VP9 SVC is still more beneficial for BW reasons.

Bug: webrtc:14884, webrtc:15005
Change-Id: I748aae1adb47acc8a6b79b5852cff6aa47a46f5d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/298046
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39601}
This commit is contained in:
Henrik Boström 2023-03-20 10:09:04 +01:00 committed by WebRTC LUCI CQ
parent 12669513d2
commit 75990b9a8f
3 changed files with 11 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
media/engine/webrtc_video_engine.cc
View File

@ -2502,9 +2502,9 @@ 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()) {

10
media/engine/webrtc_video_engine_unittest.cc
View File

@ -8463,7 +8463,9 @@ TEST_F(WebRtcVideoChannelTest,
webrtc::ScalabilityModeFromString(kDefaultScalabilityModeStr);
EXPECT_EQ(2, stream->num_encoder_reconfigurations());
webrtc::VideoEncoderConfig encoder_config = stream->GetEncoderConfig().Copy();
EXPECT_EQ(1u, encoder_config.number_of_streams);
// When `scalability_mode` has been specified on any encoding, we do not
// reduce the number of simulcast streams.
EXPECT_EQ(3u, encoder_config.number_of_streams);
EXPECT_THAT(encoder_config.simulcast_layers,
ElementsAre(Field(&webrtc::VideoStream::scalability_mode,
ScalabilityMode::kL3T3),
@ -8476,7 +8478,11 @@ TEST_F(WebRtcVideoChannelTest,
// VideoStreams are created appropriately for the simulcast case.
EXPECT_THAT(stream->GetVideoStreams(),
ElementsAre(Field(&webrtc::VideoStream::scalability_mode,
ScalabilityMode::kL3T3)));
ScalabilityMode::kL3T3),
Field(&webrtc::VideoStream::scalability_mode,
kDefaultScalabilityMode),
Field(&webrtc::VideoStream::scalability_mode,
kDefaultScalabilityMode)));
// GetParameters.
parameters = send_channel_->GetRtpSendParameters(last_ssrc_);

14
pc/peer_connection_simulcast_unittest.cc
View File

@ -60,7 +60,6 @@
#include "rtc_base/thread.h"
#include "rtc_base/unique_id_generator.h"
#include "system_wrappers/include/metrics.h"
#include "test/field_trial.h"
#include "test/gmock.h"
#include "test/gtest.h"
@ -1432,13 +1431,8 @@ 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);
@ -1503,17 +1497,9 @@ TEST_F(PeerConnectionSimulcastWithMediaFlowTests,
EXPECT_THAT(*outbound_rtps[2]->scalability_mode, StrEq("L1T3"));
}
// 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.
if (!HasSenderVideoCodecCapability(local_pc_wrapper, "AV1")) {
RTC_LOG(LS_WARNING) << "\n***\nAV1 is not available, skipping test.\n***";
return;