codec/h264/h264dec: added helper function to get first MediaPID found in a stream map

container/mts/mpegts.go

@@ -286,6 +286,19 @@ func FindPSI(d []byte) (int, map[uint16]uint8, map[string]string, error) {
 	return i, streamMap, meta, nil
 }
 
+var (
+	ErrStreamMap = errors.New("stream map is empty")
+)
+
+// FirstMediaPID returns the first PID and it's type in the given streamMap.
+func FirstMediaPID(streamMap map[uint16]uint8) (p uint16, t uint8, err error) {
+	for p, t = range streamMap {
+		return
+	}
+	err = ErrStreamMap
+	return
+}
+
 // FillPayload takes a channel and fills the packets Payload field until the
 // channel is empty or we've the packet reaches capacity
 func (p *Packet) FillPayload(data []byte) int {