Match codecs with different rate or channels

Consider clock rate and channels when matching codecs. This allows to
support codecs with the same MIME type but sample rate or channel count
that might be different from the default ones, like PCMU, PCMA, LPCM
and multiopus.

internal/fmtp/fmtp.go

@@ -8,6 +8,32 @@ import (
 	"strings"
 )
 
+func defaultClockRate(mimeType string) uint32 {
+	defaults := map[string]uint32{
+		"audio/opus": 48000,
+		"audio/pcmu": 8000,
+		"audio/pcma": 8000,
+	}
+
+	if def, ok := defaults[strings.ToLower(mimeType)]; ok {
+		return def
+	}
+
+	return 90000
+}
+
+func defaultChannels(mimeType string) uint16 {
+	defaults := map[string]uint16{
+		"audio/opus": 2,
+	}
+
+	if def, ok := defaults[strings.ToLower(mimeType)]; ok {
+		return def
+	}
+
+	return 0
+}
+
 func parseParameters(line string) map[string]string {
 	parameters := make(map[string]string)
 
@@ -24,6 +50,61 @@ func parseParameters(line string) map[string]string {
 	return parameters
 }
 
+// ClockRateEqual checks whether two clock rates are equal.
+func ClockRateEqual(mimeType string, valA, valB uint32) bool {
+	// Lots of users use formats without setting clock rate or channels.
+	// In this case, use default values.
+	// It would be better to remove this exception in a future major release.
+	if valA == 0 {
+		valA = defaultClockRate(mimeType)
+	}
+	if valB == 0 {
+		valB = defaultClockRate(mimeType)
+	}
+
+	return valA == valB
+}
+
+// ChannelsEqual checks whether two channels are equal.
+func ChannelsEqual(mimeType string, valA, valB uint16) bool {
+	// Lots of users use formats without setting clock rate or channels.
+	// In this case, use default values.
+	// It would be better to remove this exception in a future major release.
+	if valA == 0 {
+		valA = defaultChannels(mimeType)
+	}
+	if valB == 0 {
+		valB = defaultChannels(mimeType)
+	}
+
+	// RFC8866: channel count "is OPTIONAL and may be omitted
+	// if the number of channels is one".
+	if valA == 0 {
+		valA = 1
+	}
+	if valB == 0 {
+		valB = 1
+	}
+
+	return valA == valB
+}
+
+func paramsEqual(valA, valB map[string]string) bool {
+	for k, v := range valA {
+		if vb, ok := valB[k]; ok && !strings.EqualFold(vb, v) {
+			return false
+		}
+	}
+
+	for k, v := range valB {
+		if va, ok := valA[k]; ok && !strings.EqualFold(va, v) {
+			return false
+		}
+	}
+
+	return true
+}
+
 // FMTP interface for implementing custom
 // FMTP parsers based on MimeType.
 type FMTP interface {
@@ -39,7 +120,7 @@ type FMTP interface {
 }
 
 // Parse parses an fmtp string based on the MimeType.
-func Parse(mimeType, line string) FMTP {
+func Parse(mimeType string, clockRate uint32, channels uint16, line string) FMTP {
 	var fmtp FMTP
 
 	parameters := parseParameters(line)
@@ -63,6 +144,8 @@ func Parse(mimeType, line string) FMTP {
 	default:
 		fmtp = &genericFMTP{
 			mimeType:   mimeType,
+			clockRate:  clockRate,
+			channels:   channels,
 			parameters: parameters,
 		}
 	}
@@ -72,6 +155,8 @@ func Parse(mimeType, line string) FMTP {
 
 type genericFMTP struct {
 	mimeType   string
+	clockRate  uint32
+	channels   uint16
 	parameters map[string]string
 }
 
@@ -87,23 +172,10 @@ func (g *genericFMTP) Match(b FMTP) bool {
 		return false
 	}
 
-	if !strings.EqualFold(g.mimeType, fmtp.MimeType()) {
-		return false
-	}
-
-	for k, v := range g.parameters {
-		if vb, ok := fmtp.parameters[k]; ok && !strings.EqualFold(vb, v) {
-			return false
-		}
-	}
-
-	for k, v := range fmtp.parameters {
-		if va, ok := g.parameters[k]; ok && !strings.EqualFold(va, v) {
-			return false
-		}
-	}
-
-	return true
+	return strings.EqualFold(g.mimeType, fmtp.MimeType()) &&
+		ClockRateEqual(g.mimeType, g.clockRate, fmtp.clockRate) &&
+		ChannelsEqual(g.mimeType, g.channels, fmtp.channels) &&
+		paramsEqual(g.parameters, fmtp.parameters)
 }
 
 func (g *genericFMTP) Parameter(key string) (string, bool) {