media_opt_util: Update robustness settings for Hybrid mode. Updated table for the computation of the adjustment factor.

Review URL: http://webrtc-codereview.appspot.com/93013

git-svn-id: http://webrtc.googlecode.com/svn/trunk@286 4adac7df-926f-26a2-2b94-8c16560cd09d

src/modules/video_coding/main/source/media_opt_util.cc

@@ -43,19 +43,12 @@ VCMNackFecMethod::ProtectionFactor(const
                                    VCMProtectionParameters* parameters)
 {
     // Hybrid Nack FEC has three operational modes:
-    // 1. Low RTT - Nack only (Set FEC rates to zero)
+    // 1. Low RTT (below kLowRttNackMs) - Nack only: Set FEC rate
-    // 2. High RTT - FEC Only
+    //    (_protectionFactorD) to zero.
-    // 3. Medium RTT values - Hybrid ; in hybrid mode, we will only nack the
+    // 2. High RTT (above kHighRttNackMs) - FEC Only: Keep FEC factors.
-    //    residual following the decoding of the FEC (refer to JB logic)
+    // 3. Medium RTT values - Hybrid mode: We will only nack the
-
+    //    residual following the decoding of the FEC (refer to JB logic). FEC
-    // Low RTT - NACK only mode
+    //    delta protection factor will be adjusted based on the RTT.
-    if (parameters->rtt < kLowRttNackMs)
-    {
-        // Set the FEC parameters to 0
-        _protectionFactorK = 0;
-        _protectionFactorD = 0;
-        return true;
-    }
 
     // Otherwise: we count on FEC; if the RTT is below a threshold, then we
     // nack the residual, based on a decision made in the JB.
@@ -66,18 +59,22 @@ VCMNackFecMethod::ProtectionFactor(const
     _protectionFactorK = _fecMethod->_protectionFactorK;
     _protectionFactorD = _fecMethod->_protectionFactorD;
 
-    // When in Hybrid mode, correct FEC rates based on the
+    // When in Hybrid mode (RTT range), adjust FEC rates based on the
-    // RTT (NACK effectiveness)
+    // RTT (NACK effectiveness) - adjustment factor is in the range [0,1].
     if (parameters->rtt < kHighRttNackMs)
     {
         WebRtc_UWord16 rttIndex = (WebRtc_UWord16) parameters->rtt;
-        // TODO(mikhal): update table
+        float adjustRtt = (float)VCMNackFecTable[rttIndex] / 100.0f;
-        float softnessRtt = (float)VCMNackFecTable[rttIndex] / (float)4096.0;
 
-        // Soften FEC with NACK on (for delta frame only)
+        // Adjust FEC with NACK on (for delta frame only)
         // table depends on RTT relative to rttMax (NACK Threshold)
-        _protectionFactorD *= static_cast<WebRtc_UWord8> (softnessRtt);
+        _protectionFactorD = static_cast<WebRtc_UWord8>
+                            (adjustRtt *
+                             static_cast<float>(_protectionFactorD));
+        // update FEC rates after applyingadjustment softness parameter
+        _fecMethod->UpdateProtectionFactorD(_protectionFactorD);
     }
+
     return true;
 }
 
@@ -85,16 +82,6 @@ bool
 VCMNackFecMethod::EffectivePacketLoss(const
                                       VCMProtectionParameters* parameters)
 {
-    // NACK only mode
-    if (parameters->rtt < kLowRttNackMs)
-    {
-        // Effective Packet Loss, NA in current version.
-        _effectivePacketLoss = 0;
-        // No FEC applied.
-        _residualPacketLossFec = parameters->lossPr;
-        return true;
-    }
-
     // Set the effective packet loss for encoder (based on FEC code).
     // Compute the effective packet loss and residual packet loss due to FEC.
     _fecMethod->EffectivePacketLoss(parameters);
@@ -180,6 +167,14 @@ VCMFecMethod::ConvertFECRate(WebRtc_UWord8 codeRateRTP) const
                                       (float)(255 - codeRateRTP))));
 }
 
+// Update FEC with protectionFactorD
+void
+VCMFecMethod::UpdateProtectionFactorD(WebRtc_UWord8 protectionFactorD)
+{
+    _protectionFactorD = protectionFactorD;
+
+}
+
 // AvgRecoveryFEC: computes the residual packet loss function.
 // This is the average recovery from the FEC, assuming random packet loss model.
 // Computed off-line for a range of FEC code parameters and loss rates.

src/modules/video_coding/main/source/media_opt_util.h

@@ -194,6 +194,8 @@ public:
     WebRtc_UWord8 ConvertFECRate(WebRtc_UWord8 codeRate) const;
     // Get the average effective recovery from FEC: for random loss model
     float AvgRecoveryFEC(const VCMProtectionParameters* parameters) const;
+    // Update FEC with protectionFactorD
+    void UpdateProtectionFactorD(WebRtc_UWord8 protectionFactorD);
 };
 
 

src/modules/video_coding/main/source/nack_fec_tables.h

@@ -14,210 +14,111 @@
 namespace webrtc
 {
 
-// Table for softening FEC rate for NACK/FEC protection method
+// Table for adjusting FEC rate for NACK/FEC protection method
-const WebRtc_UWord16 VCMNackFecTable[200] = {
+// Table values are built as a sigmoid function, ranging from 0 to
-
+// kHighRttNackMs (100), based on the HybridNackTH values defined in
-27,
+// media_opt_util.h.
+const WebRtc_UWord16 VCMNackFecTable[100] = {
+0,
+0,
+0,
+0,
+0,
+0,
+0,
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+0,
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-
 
 };