From 99a1d06d9b809b1069ca4b76abbb4eb2e3ca3e5f Mon Sep 17 00:00:00 2001
From: xia-chu <771730766@qq.com>
Date: Thu, 22 Apr 2021 18:56:12 +0800
Subject: [PATCH] 修正TWCC错误理解
---
src/Rtcp/RtcpFCI.cpp | 49 ++++++++++++++++++++++++++++++++++++++-----------
src/Rtcp/RtcpFCI.h | 2 +-
2 files changed, 39 insertions(+), 12 deletions(-)
diff --git a/src/Rtcp/RtcpFCI.cpp b/src/Rtcp/RtcpFCI.cpp
index eec9e7f..3f465aa 100644
--- a/src/Rtcp/RtcpFCI.cpp
+++ b/src/Rtcp/RtcpFCI.cpp
@@ -261,9 +261,35 @@ uint32_t FCI_TWCC::getReferenceTime() const {
ret |= ref_time[2];
return ret;
}
-
-static uint16_t getRecvDelta(SymbolStatus status, uint8_t *&ptr, const uint8_t *end){
- uint16_t delta = 0;
+//3.1.5. Receive Delta
+//
+// Deltas are represented as multiples of 250us:
+//
+// o If the "Packet received, small delta" symbol has been appended to
+// the status list, an 8-bit unsigned receive delta will be appended
+// to recv delta list, representing a delta in the range [0, 63.75]
+// ms.
+//
+// o If the "Packet received, large or negative delta" symbol has been
+// appended to the status list, a 16-bit signed receive delta will be
+// appended to recv delta list, representing a delta in the range
+// [-8192.0, 8191.75] ms.
+//
+// o If the delta exceeds even the larger limits, a new feedback
+// message must be used, where the 24-bit base receive delta can
+// cover very large gaps.
+//
+// The smaller receive delta upper bound of 63.75 ms means that this is
+// only viable at about 1000/25.5 ~= 16 packets per second and above.
+// With a packet size of 1200 bytes/packet that amounts to a bitrate of
+// about 150 kbit/s.
+//
+// The 0.25 ms resolution means that up to 4000 packets per second can
+// be represented. With a 1200 bytes/packet payload, that amounts to
+// 38.4 Mbit/s payload bandwidth.
+
+static int16_t getRecvDelta(SymbolStatus status, uint8_t *&ptr, const uint8_t *end){
+ int16_t delta = 0;
switch (status) {
case SymbolStatus::not_received : {
//丢包， recv delta为0个字节
@@ -298,29 +324,29 @@ map<uint16_t, std::pair<SymbolStatus, uint32_t/*stamp*/> > FCI_TWCC::getPacketCh
auto end = (uint8_t *) this + total_size;
CHECK(ptr < end);
auto seq = base_seq;
- auto stamp = getReferenceTime();
for (uint8_t i = 0; i < pkt_status_count;) {
CHECK(ptr + RunLengthChunk::kSize <= end)
RunLengthChunk *chunk = (RunLengthChunk *) ptr;
if (!chunk->type) {
//RunLengthChunk
- ptr += RunLengthChunk::kSize;
for (auto j = 0; j < chunk->getRunLength(); ++j) {
- ret.emplace(seq++, std::make_pair((SymbolStatus) chunk->symbol, stamp));
- stamp += getRecvDelta((SymbolStatus) chunk->symbol, ptr, end);
+ ret.emplace(seq++, std::make_pair((SymbolStatus) chunk->symbol, 0));
++i;
}
} else {
//StatusVecChunk
StatusVecChunk *chunk = (StatusVecChunk *) ptr;
- ptr += StatusVecChunk::kSize;
for (auto &symbol : chunk->getSymbolList()) {
- ret.emplace(seq++, std::make_pair(symbol, stamp));
- stamp += getRecvDelta(symbol, ptr, end);
+ ret.emplace(seq++, std::make_pair(symbol, 0));
++i;
}
}
+ ptr += 2;
+ }
+ for (auto &pr : ret) {
+ CHECK(ptr <= end)
+ pr.second.second = 250 * getRecvDelta(pr.second.first, ptr, end);
}
return ret;
}
@@ -328,8 +354,9 @@ map<uint16_t, std::pair<SymbolStatus, uint32_t/*stamp*/> > FCI_TWCC::getPacketCh
string FCI_TWCC::dumpString(size_t total_size) const {
_StrPrinter printer;
auto map = getPacketChunkList(total_size);
+ printer << "twcc fci, base_seq:" << base_seq << ",pkt_status_count:" << pkt_status_count << ", ref time:" << getReferenceTime() << ", fb count:" << (int)fb_pkt_count << "\n";
for (auto &pr : map) {
- printer << " seq:" << pr.first <<", packet status:" << (int)(pr.second.first) << ", stamp:" << pr.second.second << "\n";
+ printer << "rtp seq:" << pr.first <<", packet status:" << (int)(pr.second.first) << ", delta:" << pr.second.second << "\n";
}
return std::move(printer);
}
diff --git a/src/Rtcp/RtcpFCI.h b/src/Rtcp/RtcpFCI.h
index 8df51f3..6676c42 100644
--- a/src/Rtcp/RtcpFCI.h
+++ b/src/Rtcp/RtcpFCI.h
@@ -406,7 +406,7 @@ public:
void net2Host(size_t total_size);
uint32_t getReferenceTime() const;
- map<uint16_t, std::pair<SymbolStatus, uint32_t/*stamp*/> > getPacketChunkList(size_t total_size) const;
+ map<uint16_t, std::pair<SymbolStatus, uint32_t/*recv delta 微秒*/> > getPacketChunkList(size_t total_size) const;
string dumpString(size_t total_size) const;
} PACKED;
--
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