Fixed unnecessary playlist version change in SetDefaultKey

writer.go

@@ -516,9 +516,16 @@ func (p *MediaPlaylist) Close() {
 // Set encryption key appeared once in header of the playlist (pointer to MediaPlaylist.Key).
 // It useful when keys not changed during playback.
 // Set tag for the whole list.
-func (p *MediaPlaylist) SetDefaultKey(method, uri, iv, keyformat, keyformatversions string) {
-	version(&p.ver, 5) // due section 7
+func (p *MediaPlaylist) SetDefaultKey(method, uri, iv, keyformat, keyformatversions string) error {
+	// A Media Playlist MUST indicate a EXT-X-VERSION of 5 or higher if it
+	// contains:
+	//   - The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY tag.
+	if keyformat != "" && keyformatversions != "" {
+		version(&p.ver, 5)
+	}
 	p.Key = &Key{method, uri, iv, keyformat, keyformatversions}
+
+	return nil
 }
 
 // Set map appeared once in header of the playlist (pointer to MediaPlaylist.Key).

writer_test.go

@@ -171,6 +171,33 @@ func TestSetKeyForMediaPlaylist(t *testing.T) {
 	}
 }
 
+// Create new media playlist
+// Add segment to media playlist
+// Set encryption key
+func TestSetDefaultKeyForMediaPlaylist(t *testing.T) {
+	p, e := NewMediaPlaylist(3, 5)
+	if e != nil {
+		t.Fatalf("Create media playlist failed: %s", e)
+	}
+	e = p.SetDefaultKey("AES-128", "https://example.com", "iv", "", "")
+	if e != nil {
+		t.Errorf("Set default key to a media playlist failed: %s", e)
+	}
+	if p.ver != 3 {
+		t.Errorf("SetDefaultKey to a media playlist changed version unnecessarily")
+	}
+
+	// Test that using V5 features updates EXT-X-VERSION
+	e = p.SetDefaultKey("AES-128", "https://example.com", "iv", "format", "vers")
+	if e != nil {
+		t.Errorf("Set key to a media playlist failed: %s", e)
+	}
+	if p.ver != 5 {
+		t.Errorf("SetDefaultKey did not update version")
+	}
+
+}
+
 // Create new media playlist
 // Add segment to media playlist
 // Set map