Add an element "CueBlockNumber" (#48)

elementtable.go

@@ -49,6 +49,7 @@ var table = elementTable{
 	ElementSeekPosition:           elementDef{[]byte{0x53, 0xAC}, TypeUInt, false},
 	ElementMuxingApp:              elementDef{[]byte{0x4D, 0x80}, TypeString, false},
 	ElementName:                   elementDef{[]byte{0x53, 0x6E}, TypeString, false},
+	ElementCueBlockNumber:         elementDef{[]byte{0x53, 0x78}, TypeUInt, false},
 	ElementCodecDelay:             elementDef{[]byte{0x56, 0xAA}, TypeUInt, false},
 	ElementSeekPreRoll:            elementDef{[]byte{0x56, 0xBB}, TypeUInt, false},
 	ElementWritingApp:             elementDef{[]byte{0x57, 0x41}, TypeString, false},

elementtype.go

@@ -120,6 +120,7 @@ const (
 	ElementCueTrackPositions
 	ElementCueTrack
 	ElementCueClusterPosition
+	ElementCueBlockNumber
 
 	elementMax
 )
@@ -296,6 +297,8 @@ func (i ElementType) String() string {
 		return "CueTrack"
 	case ElementCueClusterPosition:
 		return "CueClusterPosition"
+	case ElementCueBlockNumber:
+		return "CueBlockNumber"
 	default:
 		return "unknown"
 	}
@@ -474,6 +477,8 @@ func ElementTypeFromString(s string) (ElementType, error) {
 		return ElementCueTrack, nil
 	case "CueClusterPosition":
 		return ElementCueClusterPosition, nil
+	case "CueBlockNumber":
+		return ElementCueBlockNumber, nil
 	default:
 		return 0, errUnknownElementType
 	}

marshal_roundtrip_test.go

@@ -87,7 +87,7 @@ func TestMarshal_RoundtripWebM(t *testing.T) {
 					{
 						CueTime: 1,
 						CueTrackPositions: []webm.CueTrackPosition{
-							{CueTrack: 2, CueClusterPosition: 3},
+							{CueTrack: 2, CueClusterPosition: 3, CueBlockNumber: 4},
 						},
 					},
 				},

webm/webm.go

@@ -103,6 +103,7 @@ type CuePoint struct {
 type CueTrackPosition struct {
 	CueTrack           uint64 `ebml:"CueTrack"`
 	CueClusterPosition uint64 `ebml:"CueClusterPosition"`
+	CueBlockNumber     uint64 `ebml:"CueBlockNumber,omitempty"`
 }
 
 // Segment represents Segment element struct