diff --git a/media/engine/payload_type_mapper.cc b/media/engine/payload_type_mapper.cc
index e9f863c..8c85f02 100644
--- a/media/engine/payload_type_mapper.cc
+++ b/media/engine/payload_type_mapper.cc
@@ -32,18 +32,18 @@
       max_payload_type_(127),
       mappings_(
           {// Static payload type assignments according to RFC 3551.
-           {{"PCMU", 8000, 1}, 0},
+           {{kPcmuCodecName, 8000, 1}, 0},
            {{"GSM", 8000, 1}, 3},
            {{"G723", 8000, 1}, 4},
            {{"DVI4", 8000, 1}, 5},
            {{"DVI4", 16000, 1}, 6},
            {{"LPC", 8000, 1}, 7},
-           {{"PCMA", 8000, 1}, 8},
-           {{"G722", 8000, 1}, 9},
-           {{"L16", 44100, 2}, 10},
-           {{"L16", 44100, 1}, 11},
+           {{kPcmaCodecName, 8000, 1}, 8},
+           {{kG722CodecName, 8000, 1}, 9},
+           {{kL16CodecName, 44100, 2}, 10},
+           {{kL16CodecName, 44100, 1}, 11},
            {{"QCELP", 8000, 1}, 12},
-           {{"CN", 8000, 1}, 13},
+           {{kCnCodecName, 8000, 1}, 13},
            // RFC 4566 is a bit ambiguous on the contents of the "encoding
            // parameters" field, which, for audio, encodes the number of
            // channels. It is "optional and may be omitted if the number of
@@ -70,7 +70,8 @@
            {{kOpusCodecName,
              48000,
              2,
-             {{"minptime", "10"}, {"useinbandfec", "1"}}},
+             {{kCodecParamMinPTime, "10"},
+              {kCodecParamUseInbandFec, kParamValueTrue}}},
             111},
            // TODO(solenberg): Remove the hard coded 16k,32k,48k DTMF once we
            // assign payload types dynamically for send side as well.