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修正TWCC错误理解

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This commit is contained in:
xia-chu 2021-04-22 18:56:12 +08:00
parent 90ad90cb78
commit 99a1d06d9b
2 changed files with 38 additions and 11 deletions
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47
src/Rtcp/RtcpFCI.cpp
View File

@ -261,9 +261,35 @@ uint32_t FCI_TWCC::getReferenceTime() const {
ret |= ref_time[2];
return ret;
}
//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 uint16_t getRecvDelta(SymbolStatus status, uint8_t *&ptr, const uint8_t *end){
uint16_t delta = 0;
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);
}

2
src/Rtcp/RtcpFCI.h
View File

@ -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;