stream: added GetDst func to Encoder interface

It has become apparent that it would be useful to be able to get the destination from
the encoder, so this it at least a temporary fix.

stream/encoding.go

@@ -31,6 +31,7 @@ import "io"
 
 type Encoder interface {
 	Write([]byte) (int, error)
+	GetDst() io.Writer
 }
 
 // NopEncoder returns an
@@ -47,3 +48,5 @@ func (e noop) Write(p []byte) (int, error) {
 	n, err := e.dst.Write(p)
 	return n, err
 }
+
+func (e noop) GetDst() io.Writer { return e.dst }

stream/flv/encoder.go

@@ -261,3 +261,5 @@ func (e *Encoder) Write(frame []byte) (int, error) {
 
 	return len(frame), nil
 }
+
+func (e *Encoder) GetDst() io.Writer { return e.dst }

stream/mts/encoder.go

@@ -232,6 +232,8 @@ func (e *Encoder) Write(nalu []byte) (int, error) {
 	return len(nalu), nil
 }
 
+func (e *Encoder) GetDst() io.Writer { return e.dst }
+
 // writePSI creates mpegts with pat and pmt tables - with pmt table having updated
 // location and time data.
 func (e *Encoder) writePSI() error {