diff --git a/main.go b/main.go
index ca4416d..3ae5dde 100644
--- a/main.go
+++ b/main.go
@@ -13,6 +13,7 @@ import (
 )
 
 const DefaultTargetDuration = 3 * time.Second
+const DefaultPlaylistDuration = 20 * time.Second
 
 type Segment struct {
 	targetDuration time.Duration
@@ -96,7 +97,7 @@ func (s *MP3HTTPSegmenter) Segment(r io.Reader) (chan *Segment, error) {
 			}
 
 			if n != int64(v.Size()) {
-				// TODO would this ever happen?
+				// TODO would this ever happen? What should IncrementDuration be called with?
 				log.Fatal("unexpeced frame size, want = ", v.Size(), "got = ", n)
 			}
 
@@ -115,6 +116,7 @@ type Playlist interface {
 	// These could be moved to an interface?
 	Duration() time.Duration
 	TargetDuration() time.Duration
+	AddSegment(s *Segment) error
 }
 
 type MediaPlaylist struct {
@@ -128,8 +130,33 @@ func newMediaPlaylist() *MediaPlaylist {
 }
 
 func (p *MediaPlaylist) Duration() time.Duration {
+	return p.durationOf(p.Segments)
+}
+
+func (p *MediaPlaylist) TargetDuration() time.Duration {
+	return DefaultPlaylistDuration
+}
+
+func (p *MediaPlaylist) AddSegment(s *Segment) error {
+	p.Segments = append(p.Segments, s)
+
+	if len(p.Segments) == 1 {
+		return nil
+	}
+
+	for {
+		if p.durationOf(p.Segments[1:]) > p.TargetDuration() {
+			p.Segments = p.Segments[1:]
+		}
+		break
+	}
+
+	return nil
+}
+
+func (p *MediaPlaylist) durationOf(ss []*Segment) time.Duration {
 	var t time.Duration
-	for _, s := range p.Segments {
+	for _, s := range ss {
 		t += s.Duration()
 	}
 	return t
@@ -144,6 +171,11 @@ func (p *MediaPlaylist) Run() error {
 	}
 }
 
+type PlaylistListener interface {
+	SegmentAdded(s *Segment) error
+	SegmentRemoved(s *Segment) error
+}
+
 func main() {
 	// TODO accept some flags with:
 	// URL - source of stream
diff --git a/main_test.go b/main_test.go
index a7f30fd..ff0fb2a 100644
--- a/main_test.go
+++ b/main_test.go
@@ -20,3 +20,18 @@ func TestSegment(t *testing.T) {
 	require.Equal(t, 10*time.Second, segment.Duration())
 	require.False(t, segment.CanWrite(1*time.Millisecond))
 }
+
+func TestMediaPlaylistImplements(t *testing.T) {
+	require.Implements(t, (*Playlist)(nil), newMediaPlaylist())
+}
+
+func TestMediaPlaylist(t *testing.T) {
+	playlist := newMediaPlaylist()
+
+	for i := 0; i < 8; i++ {
+		s := newSegment(10*time.Second, 0)
+		s.IncrementDuration(3 * time.Second)
+		playlist.AddSegment(s)
+	}
+	require.Equal(t, 21*time.Second, playlist.Duration())
+}