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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 "modules/rtp_rtcp/source/tmmbr_help.h"
#include <stddef.h>
#include <limits>
#include "absl/algorithm/container.h"
#include "rtc_base/checks.h"
namespace webrtc {
std::vector<rtcp::TmmbItem> TMMBRHelp::FindBoundingSet(
std::vector<rtcp::TmmbItem> candidates) {
// Filter out candidates with 0 bitrate.
for (auto it = candidates.begin(); it != candidates.end();) {
if (!it->bitrate_bps())
it = candidates.erase(it);
else
++it;
}
if (candidates.size() <= 1)
return candidates;
size_t num_candidates = candidates.size();
// 1. Sort by increasing packet overhead.
absl::c_sort(candidates,
[](const rtcp::TmmbItem& lhs, const rtcp::TmmbItem& rhs) {
return lhs.packet_overhead() < rhs.packet_overhead();
});
// 2. For tuples with same overhead, keep the one with the lowest bitrate.
for (auto it = candidates.begin(); it != candidates.end();) {
RTC_DCHECK(it->bitrate_bps());
auto current_min = it;
auto next_it = it + 1;
// Use fact candidates are sorted by overhead, so candidates with same
// overhead are adjusted.
while (next_it != candidates.end() &&
next_it->packet_overhead() == current_min->packet_overhead()) {
if (next_it->bitrate_bps() < current_min->bitrate_bps()) {
current_min->set_bitrate_bps(0);
current_min = next_it;
} else {
next_it->set_bitrate_bps(0);
}
++next_it;
--num_candidates;
}
it = next_it;
}
// 3. Select and remove tuple with lowest bitrate.
// (If more than 1, choose the one with highest overhead).
auto min_bitrate_it = candidates.end();
for (auto it = candidates.begin(); it != candidates.end(); ++it) {
if (it->bitrate_bps()) {
min_bitrate_it = it;
break;
}
}
for (auto it = min_bitrate_it; it != candidates.end(); ++it) {
if (it->bitrate_bps() &&
it->bitrate_bps() <= min_bitrate_it->bitrate_bps()) {
// Get min bitrate.
min_bitrate_it = it;
}
}
std::vector<rtcp::TmmbItem> bounding_set;
bounding_set.reserve(num_candidates);
std::vector<float> intersection(num_candidates);
std::vector<float> max_packet_rate(num_candidates);
// First member of selected list.
bounding_set.push_back(*min_bitrate_it);
intersection[0] = 0;
// Calculate its maximum packet rate (where its line crosses x-axis).
uint16_t packet_overhead = bounding_set.back().packet_overhead();
if (packet_overhead == 0) {
// Avoid division by zero.
max_packet_rate[0] = std::numeric_limits<float>::max();
} else {
max_packet_rate[0] =
bounding_set.back().bitrate_bps() / static_cast<float>(packet_overhead);
}
// Remove from candidate list.
min_bitrate_it->set_bitrate_bps(0);
--num_candidates;
// 4. Discard from candidate list all tuple with lower overhead
// (next tuple must be steeper).
for (auto it = candidates.begin(); it != candidates.end(); ++it) {
if (it->bitrate_bps() &&
it->packet_overhead() < bounding_set.front().packet_overhead()) {
it->set_bitrate_bps(0);
--num_candidates;
}
}
bool get_new_candidate = true;
rtcp::TmmbItem cur_candidate;
while (num_candidates > 0) {
if (get_new_candidate) {
// 5. Remove first remaining tuple from candidate list.
for (auto it = candidates.begin(); it != candidates.end(); ++it) {
if (it->bitrate_bps()) {
cur_candidate = *it;
it->set_bitrate_bps(0);
break;
}
}
}
// 6. Calculate packet rate and intersection of the current
// line with line of last tuple in selected list.
RTC_DCHECK_NE(cur_candidate.packet_overhead(),
bounding_set.back().packet_overhead());
float packet_rate = static_cast<float>(cur_candidate.bitrate_bps() -
bounding_set.back().bitrate_bps()) /
(cur_candidate.packet_overhead() -
bounding_set.back().packet_overhead());
// 7. If the packet rate is equal or lower than intersection of
// last tuple in selected list,
// remove last tuple in selected list & go back to step 6.
if (packet_rate <= intersection[bounding_set.size() - 1]) {
// Remove last tuple and goto step 6.
bounding_set.pop_back();
get_new_candidate = false;
} else {
// 8. If packet rate is lower than maximum packet rate of
// last tuple in selected list, add current tuple to selected
// list.
if (packet_rate < max_packet_rate[bounding_set.size() - 1]) {
bounding_set.push_back(cur_candidate);
intersection[bounding_set.size() - 1] = packet_rate;
uint16_t packet_overhead = bounding_set.back().packet_overhead();
RTC_DCHECK_NE(packet_overhead, 0);
max_packet_rate[bounding_set.size() - 1] =
bounding_set.back().bitrate_bps() /
static_cast<float>(packet_overhead);
}
--num_candidates;
get_new_candidate = true;
}
// 9. Go back to step 5 if any tuple remains in candidate list.
}
RTC_DCHECK(!bounding_set.empty());
return bounding_set;
}
bool TMMBRHelp::IsOwner(const std::vector<rtcp::TmmbItem>& bounding,
uint32_t ssrc) {
for (const rtcp::TmmbItem& item : bounding) {
if (item.ssrc() == ssrc) {
return true;
}
}
return false;
}
uint64_t TMMBRHelp::CalcMinBitrateBps(
const std::vector<rtcp::TmmbItem>& candidates) {
RTC_DCHECK(!candidates.empty());
uint64_t min_bitrate_bps = std::numeric_limits<uint64_t>::max();
for (const rtcp::TmmbItem& item : candidates)
if (item.bitrate_bps() < min_bitrate_bps)
min_bitrate_bps = item.bitrate_bps();
return min_bitrate_bps;
}
} // namespace webrtc
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