Some re-organization of the fec-uep code: updated protection modes, comments, and some variable/function re-naming.
Review URL: http://webrtc-codereview.appspot.com/231001 git-svn-id: http://webrtc.googlecode.com/svn/trunk@752 4adac7df-926f-26a2-2b94-8c16560cd09d
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marpan@webrtc.org
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55c39f0940
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14aaaf116a
@ -16,15 +16,14 @@
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namespace {
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// Allow for two different modes of protection for residual packets.
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// The residual packets are the remaining packets beyond the important ones.
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enum ResidualProtectionMode
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// Allow for different modes of protection for packets in UEP case.
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enum ProtectionMode
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{
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kModeNoOverlap,
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kModeOverlap,
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kModeBiasFirstPacket,
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};
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/**
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* Fits an input mask (subMask) to an output mask.
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* The mask is a matrix where the rows are the FEC packets,
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@ -158,12 +157,12 @@ void ShiftFitSubMask(WebRtc_UWord16 numMaskBytes,
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namespace webrtc {
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namespace internal {
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// Residual protection for remaining packets
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void ResidualPacketProtection(WebRtc_UWord16 numMediaPackets,
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WebRtc_UWord16 numFecPackets,
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WebRtc_UWord16 numImpPackets,
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// Remaining protection after important (first partition) packet protection
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void RemainingPacketProtection(WebRtc_UWord16 numMediaPackets,
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WebRtc_UWord16 numFecRemaining,
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WebRtc_UWord16 numFecForImpPackets,
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WebRtc_UWord16 numMaskBytes,
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ResidualProtectionMode mode,
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ProtectionMode mode,
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WebRtc_UWord8* packetMask)
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{
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if (mode == kModeNoOverlap)
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@ -171,34 +170,38 @@ void ResidualPacketProtection(WebRtc_UWord16 numMediaPackets,
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// subMask21
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const WebRtc_UWord8 lBit =
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(numMediaPackets - numImpPackets) > 16 ? 1 : 0;
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(numMediaPackets - numFecForImpPackets) > 16 ? 1 : 0;
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const WebRtc_UWord16 resMaskBytes =
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(lBit == 1)? kMaskSizeLBitSet : kMaskSizeLBitClear;
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const WebRtc_UWord8* packetMaskSub21 =
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packetMaskTbl[numMediaPackets - numImpPackets - 1]
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[numFecPackets - numImpPackets - 1];
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packetMaskTbl[numMediaPackets - numFecForImpPackets - 1]
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[numFecRemaining - 1];
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ShiftFitSubMask(numMaskBytes, resMaskBytes,
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numImpPackets, numFecPackets,
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ShiftFitSubMask(numMaskBytes, resMaskBytes, numFecForImpPackets,
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(numFecForImpPackets + numFecRemaining),
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packetMaskSub21, packetMask);
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}
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else if (mode == kModeOverlap)
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else if (mode == kModeOverlap || mode == kModeBiasFirstPacket)
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{
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// subMask22
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const WebRtc_UWord16 numFecForResidual =
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numFecPackets - numImpPackets;
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const WebRtc_UWord8* packetMaskSub22 =
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packetMaskTbl[numMediaPackets - 1]
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[numFecForResidual - 1];
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packetMaskTbl[numMediaPackets - 1][numFecRemaining - 1];
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FitSubMask(numMaskBytes, numMaskBytes,
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numFecForResidual,
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packetMaskSub22,
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&packetMask[numImpPackets * numMaskBytes]);
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FitSubMask(numMaskBytes, numMaskBytes, numFecRemaining, packetMaskSub22,
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&packetMask[numFecForImpPackets * numMaskBytes]);
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if (mode == kModeBiasFirstPacket)
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{
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for (WebRtc_UWord32 i = 0; i < numFecRemaining; i++)
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{
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WebRtc_UWord32 pktMaskIdx = i * numMaskBytes;
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packetMask[pktMaskIdx] = packetMask[pktMaskIdx] | (1 << 7);
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}
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}
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}
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else
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{
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@ -207,8 +210,8 @@ void ResidualPacketProtection(WebRtc_UWord16 numMediaPackets,
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}
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// Higher protection for numImpPackets
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void ImportantPacketProtection(WebRtc_UWord16 numFecPackets,
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// Protection for important (first partition) packets
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void ImportantPacketProtection(WebRtc_UWord16 numFecForImpPackets,
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WebRtc_UWord16 numImpPackets,
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WebRtc_UWord16 numMaskBytes,
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WebRtc_UWord8* packetMask)
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@ -217,72 +220,127 @@ void ImportantPacketProtection(WebRtc_UWord16 numFecPackets,
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const WebRtc_UWord16 numImpMaskBytes =
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(lBit == 1)? kMaskSizeLBitSet : kMaskSizeLBitClear;
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WebRtc_UWord32 numFecForImpPackets = numImpPackets;
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if (numFecPackets < numImpPackets)
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{
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numFecForImpPackets = numFecPackets;
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}
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// Get subMask1 from table
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const WebRtc_UWord8* packetMaskSub1 =
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packetMaskTbl[numImpPackets - 1][numFecForImpPackets - 1];
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FitSubMask(numMaskBytes, numImpMaskBytes,
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numFecForImpPackets,
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packetMaskSub1,
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packetMask);
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numFecForImpPackets, packetMaskSub1, packetMask);
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}
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// Modification for UEP: reuse the tables (designed for equal protection).
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// First version is to build mask from two sub-masks.
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// Longer-term, may add another set of tables for UEP cases for more
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// flexibility in protection between important and residual packets.
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// This function sets the protection allocation: i.e., how many FEC packets
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// to use for numImp (1st partition) packets, given the: number of media
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// packets, number of FEC packets, and number of 1st partition packets.
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WebRtc_UWord32 SetProtectionAllocation(const WebRtc_UWord16 numMediaPackets,
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const WebRtc_UWord16 numFecPackets,
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const WebRtc_UWord16 numImpPackets)
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{
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// UEP scheme:
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// First subMask is for higher protection for important packets.
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// Other subMask is the residual protection for remaining packets.
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// TODO (marpan): test different cases for protection allocation:
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// Use at most (allocPar * numFecPackets) for important packets.
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float allocPar = 0.5;
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WebRtc_UWord16 maxNumFecForImp = static_cast<WebRtc_UWord16>
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(allocPar * numFecPackets);
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WebRtc_UWord16 numFecForImpPackets = (numImpPackets < maxNumFecForImp) ?
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numImpPackets : maxNumFecForImp;
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// Fall back to equal protection in this case
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if (numFecPackets == 1 && (numMediaPackets > 2 * numImpPackets))
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{
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numFecForImpPackets = 0;
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}
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return numFecForImpPackets;
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}
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// Modification for UEP: reuse the off-line tables for the packet masks.
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// Note: these masks were designed for equal packet protection case,
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// assuming random packet loss.
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// Current version has 3 modes (options) to build UEP mask from existing ones.
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// Various other combinations may be added in future versions.
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// Longer-term, we may add another set of tables specifically for UEP cases.
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// TODO (marpan): also consider modification of masks for bursty loss cases.
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// Mask is characterized as (#packets_to_protect, #fec_for_protection).
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// Protection defined as: (#fec_for_protection / #packets_to_protect).
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// Protection factor defined as: (#fec_for_protection / #packets_to_protect).
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// So if k = numMediaPackets, n=total#packets, (n-k)=numFecPackets,
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// and m=numImpPackets, then we will have the following:
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// Let k=numMediaPackets, n=total#packets, (n-k)=numFecPackets, m=numImpPackets.
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// For important packets:
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// subMask1 = (m, t): protection = m/(t), where t=min(m,n-k).
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// For ProtectionMode 0 and 1:
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// one mask (subMask1) is used for 1st partition packets,
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// the other mask (subMask21/22, for 0/1) is for the remaining FEC packets.
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// For the residual protection, we currently have two options:
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// In both mode 0 and 1, the packets of 1st partition (numImpPackets) are
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// treated equally important, and are afforded more protection than the
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// residual partition packets.
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// Mode 0: subMask21 = (k-m,n-k-m): protection = (n-k-m)/(k-m):
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// no protection overlap between the two partitions.
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// For numImpPackets:
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// subMask1 = (m, t): protection = t/(m), where t=F(k,n-k,m).
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// t=F(k,n-k,m) is the number of packets used to protect first partition in
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// subMask1. This is determined from the function SetProtectionAllocation().
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// Mode 1: subMask22 = (k, n-k-m), with protection (n-k-m)/(k):
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// some protection overlap between the two partitions.
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// For the left-over protection:
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// Mode 0: subMask21 = (k-m,n-k-t): protection = (n-k-t)/(k-m)
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// mode 0 has no protection overlap between the two partitions.
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// For mode 0, we would typically set t = min(m, n-k).
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// Mode 1: subMask22 = (k, n-k-t), with protection (n-k-t)/(k)
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// mode 1 has protection overlap between the two partitions (preferred).
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// For ProtectionMode 2:
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// This gives 1st packet of list (which is 1st packet of 1st partition) more
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// protection. In mode 2, the equal protection mask (which is obtained from
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// mode 1 for t=0) is modified (more "1s" added in 1st column of packet mask)
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// to bias higher protection for the 1st source packet.
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// Protection Mode 2 may be extended for a sort of sliding protection
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// (i.e., vary the number/density of "1s" across columns) across packets.
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void UnequalProtectionMask(const WebRtc_UWord16 numMediaPackets,
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const WebRtc_UWord16 numFecPackets,
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const WebRtc_UWord16 numImpPackets,
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const WebRtc_UWord16 numMaskBytes,
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const ResidualProtectionMode mode,
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WebRtc_UWord8* packetMask)
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{
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//
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// Generate subMask1: higher protection for numImpPackets:
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//
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ImportantPacketProtection(numFecPackets, numImpPackets,
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numMaskBytes, packetMask);
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// Set Protection type and allocation
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// TODO (marpan): test/update for best mode and some combinations thereof.
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//
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// Generate subMask2: left-over protection (for remaining partition data),
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// if we still have some some FEC packets
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//
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if (numFecPackets > numImpPackets)
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ProtectionMode mode = kModeOverlap;
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WebRtc_UWord16 numFecForImpPackets = 0;
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if (mode != kModeBiasFirstPacket)
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{
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numFecForImpPackets = SetProtectionAllocation(numMediaPackets,
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numFecPackets,
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numImpPackets);
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}
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ResidualPacketProtection(numMediaPackets,numFecPackets,
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numImpPackets, numMaskBytes,
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WebRtc_UWord16 numFecRemaining = numFecPackets - numFecForImpPackets;
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// Done with setting protection type and allocation
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//
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// Generate subMask1
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//
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if (numFecForImpPackets > 0)
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{
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ImportantPacketProtection(numFecForImpPackets, numImpPackets,
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numMaskBytes, packetMask);
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}
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//
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// Generate subMask2
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//
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if (numFecRemaining > 0)
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{
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RemainingPacketProtection(numMediaPackets, numFecRemaining,
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numFecForImpPackets, numMaskBytes,
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mode, packetMask);
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}
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@ -304,15 +362,8 @@ void GeneratePacketMasks(int numMediaPackets,
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const WebRtc_UWord16 numMaskBytes =
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(lBit == 1)? kMaskSizeLBitSet : kMaskSizeLBitClear;
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// Default: use overlap mode for residual protection.
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const ResidualProtectionMode kResidualProtectionMode = kModeOverlap;
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// Force equal-protection for these cases.
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// Equal protection is also used for: (numImpPackets == 1 && numFecPackets == 1).
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// UEP=off would generally be more efficient than the UEP=on for this case.
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// TODO (marpan): check/test this condition.
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if (!useUnequalProtection || numImpPackets == 0 ||
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(numImpPackets == 1 && numFecPackets == 1))
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// Equal-protection for these cases
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if (!useUnequalProtection || numImpPackets == 0)
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{
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// Retrieve corresponding mask table directly:for equal-protection case.
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// Mask = (k,n-k), with protection factor = (n-k)/k,
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@ -323,8 +374,7 @@ void GeneratePacketMasks(int numMediaPackets,
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else //UEP case
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{
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UnequalProtectionMask(numMediaPackets, numFecPackets, numImpPackets,
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numMaskBytes, kResidualProtectionMode,
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packetMask);
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numMaskBytes, packetMask);
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} // End of UEP modification
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