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webrtc/rtc_base/rate_statistics_unittest.cc
Yun Zhang 4774a9fcb8 Fix rate statistic when time window running out of samples 
Current rate statistic tracker has assumption, the tracking window will
always be full after first filled up. This assumption looks not always
true. One example is the input_framerate_ tracker inside
video_stream_sender.cc which is used for setup frame droper and encoder.
Whenever there is a gap in video stream, like mute/unmute,
pacer pause/unpause etc. The fps detected from the rate_statistics
becomes samples_filled_partial_window / full_window_size, which could
be extremely low for a while. This creates a misalignment between the
fps we told encoder/frame dropper, and the real fps we fed into them,
which causes short-term serious overshot and very bad experience on
delay, avsync, congestion etc. This may also depends on how fast
encoder could react to the gap between set fps and real fps, but
libvpx and openh264 at least cannot handle this well.

So propose a fix to update first timestamp after tracker window
drained. This will give more accurate fps estimate similar based on
active window after sample gets drained

Bug: webrtc:13403
Change-Id: I96792c11091fe8bfa63e669f4360a3b3e95593e1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/237720
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35447}
2021-11-30 23:57:40 +00:00

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/*
* Copyright (c) 2012 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 "rtc_base/rate_statistics.h"
#include <cstdlib>
#include "test/gtest.h"
namespace {
using webrtc::RateStatistics;
const int64_t kWindowMs = 500;
class RateStatisticsTest : public ::testing::Test {
protected:
RateStatisticsTest() : stats_(kWindowMs, 8000) {}
RateStatistics stats_;
};
TEST_F(RateStatisticsTest, TestStrictMode) {
int64_t now_ms = 0;
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
const uint32_t kPacketSize = 1500u;
const uint32_t kExpectedRateBps = kPacketSize * 1000 * 8;
// Single data point is not enough for valid estimate.
stats_.Update(kPacketSize, now_ms++);
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
// Expecting 1200 kbps since the window is initially kept small and grows as
// we have more data.
stats_.Update(kPacketSize, now_ms);
EXPECT_EQ(kExpectedRateBps, *stats_.Rate(now_ms));
stats_.Reset();
// Expecting 0 after init.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
const int kInterval = 10;
for (int i = 0; i < 100000; ++i) {
if (i % kInterval == 0)
stats_.Update(kPacketSize, now_ms);
// Approximately 1200 kbps expected. Not exact since when packets
// are removed we will jump 10 ms to the next packet.
if (i > kInterval) {
absl::optional<uint32_t> rate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(rate));
uint32_t samples = i / kInterval + 1;
uint64_t total_bits = samples * kPacketSize * 8;
uint32_t rate_bps = static_cast<uint32_t>((1000 * total_bits) / (i + 1));
EXPECT_NEAR(rate_bps, *rate, 22000u);
}
now_ms += 1;
}
now_ms += kWindowMs;
// The window is 2 seconds. If nothing has been received for that time
// the estimate should be 0.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
}
TEST_F(RateStatisticsTest, IncreasingThenDecreasingBitrate) {
int64_t now_ms = 0;
stats_.Reset();
// Expecting 0 after init.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
stats_.Update(1000, ++now_ms);
const uint32_t kExpectedBitrate = 8000000;
// 1000 bytes per millisecond until plateau is reached.
int prev_error = kExpectedBitrate;
absl::optional<uint32_t> bitrate;
while (++now_ms < 10000) {
stats_.Update(1000, now_ms);
bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
int error = kExpectedBitrate - *bitrate;
error = std::abs(error);
// Expect the estimation error to decrease as the window is extended.
EXPECT_LE(error, prev_error + 1);
prev_error = error;
}
// Window filled, expect to be close to 8000000.
EXPECT_EQ(kExpectedBitrate, *bitrate);
// 1000 bytes per millisecond until 10-second mark, 8000 kbps expected.
while (++now_ms < 10000) {
stats_.Update(1000, now_ms);
bitrate = stats_.Rate(now_ms);
EXPECT_EQ(kExpectedBitrate, *bitrate);
}
// Zero bytes per millisecond until 0 is reached.
while (++now_ms < 20000) {
stats_.Update(0, now_ms);
absl::optional<uint32_t> new_bitrate = stats_.Rate(now_ms);
if (static_cast<bool>(new_bitrate) && *new_bitrate != *bitrate) {
// New bitrate must be lower than previous one.
EXPECT_LT(*new_bitrate, *bitrate);
} else {
// 0 kbps expected.
EXPECT_EQ(0u, *new_bitrate);
break;
}
bitrate = new_bitrate;
}
// Zero bytes per millisecond until 20-second mark, 0 kbps expected.
while (++now_ms < 20000) {
stats_.Update(0, now_ms);
EXPECT_EQ(0u, *stats_.Rate(now_ms));
}
}
TEST_F(RateStatisticsTest, ResetAfterSilence) {
int64_t now_ms = 0;
stats_.Reset();
// Expecting 0 after init.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
const uint32_t kExpectedBitrate = 8000000;
// 1000 bytes per millisecond until the window has been filled.
int prev_error = kExpectedBitrate;
absl::optional<uint32_t> bitrate;
while (++now_ms < 10000) {
stats_.Update(1000, now_ms);
bitrate = stats_.Rate(now_ms);
if (bitrate) {
int error = kExpectedBitrate - *bitrate;
error = std::abs(error);
// Expect the estimation error to decrease as the window is extended.
EXPECT_LE(error, prev_error + 1);
prev_error = error;
}
}
// Window filled, expect to be close to 8000000.
EXPECT_EQ(kExpectedBitrate, *bitrate);
now_ms += kWindowMs + 1;
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
// Silence over window size should trigger auto reset for coming sample.
stats_.Update(1000, now_ms);
++now_ms;
stats_.Update(1000, now_ms);
// We expect two samples of 1000 bytes, and that the bitrate is measured over
// active window instead of full window, which is now_ms - first_timestamp + 1
EXPECT_EQ(kExpectedBitrate, *stats_.Rate(now_ms));
// Manual reset, add the same samples again.
stats_.Reset();
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
stats_.Update(1000, now_ms);
++now_ms;
stats_.Update(1000, now_ms);
// We expect two samples of 1000 bytes, and that the bitrate is measured over
// 2 ms (window size has been reset) i.e. 2 * 8 * 1000 / 0.002 = 8000000.
EXPECT_EQ(kExpectedBitrate, *stats_.Rate(now_ms));
}
TEST_F(RateStatisticsTest, HandlesChangingWindowSize) {
int64_t now_ms = 0;
stats_.Reset();
// Sanity test window size.
EXPECT_TRUE(stats_.SetWindowSize(kWindowMs, now_ms));
EXPECT_FALSE(stats_.SetWindowSize(kWindowMs + 1, now_ms));
EXPECT_FALSE(stats_.SetWindowSize(0, now_ms));
EXPECT_TRUE(stats_.SetWindowSize(1, now_ms));
EXPECT_TRUE(stats_.SetWindowSize(kWindowMs, now_ms));
// Fill the buffer at a rate of 1 byte / millisecond (8 kbps).
const int kBatchSize = 10;
for (int i = 0; i <= kWindowMs; i += kBatchSize)
stats_.Update(kBatchSize, now_ms += kBatchSize);
EXPECT_EQ(static_cast<uint32_t>(8000), *stats_.Rate(now_ms));
// Halve the window size, rate should stay the same.
EXPECT_TRUE(stats_.SetWindowSize(kWindowMs / 2, now_ms));
EXPECT_EQ(static_cast<uint32_t>(8000), *stats_.Rate(now_ms));
// Double the window size again, rate should stay the same. (As the window
// won't actually expand until new bit and bobs fall into it.
EXPECT_TRUE(stats_.SetWindowSize(kWindowMs, now_ms));
EXPECT_EQ(static_cast<uint32_t>(8000), *stats_.Rate(now_ms));
// Fill the now empty half with bits it twice the rate.
for (int i = 0; i < kWindowMs / 2; i += kBatchSize)
stats_.Update(kBatchSize * 2, now_ms += kBatchSize);
// Rate should have increase be 50%.
EXPECT_EQ(static_cast<uint32_t>((8000 * 3) / 2), *stats_.Rate(now_ms));
}
TEST_F(RateStatisticsTest, RespectsWindowSizeEdges) {
int64_t now_ms = 0;
stats_.Reset();
// Expecting 0 after init.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
// One byte per ms, using one big sample.
stats_.Update(kWindowMs, now_ms);
now_ms += kWindowMs - 2;
// Shouldn't work! (Only one sample, not full window size.)
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
// Window size should be full, and the single data point should be accepted.
++now_ms;
absl::optional<uint32_t> bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(1000 * 8u, *bitrate);
// Add another, now we have twice the bitrate.
stats_.Update(kWindowMs, now_ms);
bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(2 * 1000 * 8u, *bitrate);
// Now that first sample should drop out...
now_ms += 1;
bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(1000 * 8u, *bitrate);
}
TEST_F(RateStatisticsTest, HandlesZeroCounts) {
int64_t now_ms = 0;
stats_.Reset();
// Expecting 0 after init.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
stats_.Update(kWindowMs, now_ms);
now_ms += kWindowMs - 1;
stats_.Update(0, now_ms);
absl::optional<uint32_t> bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(1000 * 8u, *bitrate);
// Move window along so first data point falls out.
++now_ms;
bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(0u, *bitrate);
// Move window so last data point falls out.
now_ms += kWindowMs;
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
}
TEST_F(RateStatisticsTest, HandlesQuietPeriods) {
int64_t now_ms = 0;
stats_.Reset();
// Expecting 0 after init.
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
stats_.Update(0, now_ms);
now_ms += kWindowMs - 1;
absl::optional<uint32_t> bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(0u, *bitrate);
// Move window along so first data point falls out.
++now_ms;
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
// Move window a long way out.
// This will cause an automatic reset of the window
// First data point won't give a valid result
now_ms += 2 * kWindowMs;
stats_.Update(0, now_ms);
bitrate = stats_.Rate(now_ms);
EXPECT_FALSE(static_cast<bool>(stats_.Rate(now_ms)));
// Second data point gives valid result
++now_ms;
stats_.Update(0, now_ms);
bitrate = stats_.Rate(now_ms);
EXPECT_TRUE(static_cast<bool>(bitrate));
EXPECT_EQ(0u, *bitrate);
}
TEST_F(RateStatisticsTest, HandlesBigNumbers) {
int64_t large_number = 0x100000000u;
int64_t now_ms = 0;
stats_.Update(large_number, now_ms++);
stats_.Update(large_number, now_ms);
EXPECT_TRUE(stats_.Rate(now_ms));
EXPECT_EQ(large_number * RateStatistics::kBpsScale, *stats_.Rate(now_ms));
}
TEST_F(RateStatisticsTest, HandlesTooLargeNumbers) {
int64_t very_large_number = std::numeric_limits<int64_t>::max();
int64_t now_ms = 0;
stats_.Update(very_large_number, now_ms++);
stats_.Update(very_large_number, now_ms);
// This should overflow the internal accumulator.
EXPECT_FALSE(stats_.Rate(now_ms));
}
TEST_F(RateStatisticsTest, HandlesSomewhatLargeNumbers) {
int64_t very_large_number = std::numeric_limits<int64_t>::max();
int64_t now_ms = 0;
stats_.Update(very_large_number / 4, now_ms++);
stats_.Update(very_large_number / 4, now_ms);
// This should generate a rate of more than int64_t max, but still
// accumulate less than int64_t overflow.
EXPECT_FALSE(stats_.Rate(now_ms));
}
} // namespace
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