merge format and formatdecenc into formats (#222)

pkg/formats/rtpmjpeg/headers/quantization_table.go

@@ -0,0 +1,49 @@
+package headers
+
+import (
+	"fmt"
+)
+
+// QuantizationTable is a Quantization Table header.
+type QuantizationTable struct {
+	MBZ       uint8
+	Precision uint8
+	Tables    []byte
+}
+
+// Unmarshal decodes the header.
+func (h *QuantizationTable) Unmarshal(byts []byte) (int, error) {
+	if len(byts) < 4 {
+		return 0, fmt.Errorf("buffer is too short")
+	}
+
+	h.MBZ = byts[0]
+	h.Precision = byts[1]
+	if h.Precision != 0 {
+		return 0, fmt.Errorf("Precision %d is not supported", h.Precision)
+	}
+
+	length := int(byts[2])<<8 | int(byts[3])
+	switch length {
+	case 64, 128:
+	default:
+		return 0, fmt.Errorf("Quantization table length %d is not supported", length)
+	}
+
+	if (len(byts) - 4) < length {
+		return 0, fmt.Errorf("buffer is too short")
+	}
+
+	h.Tables = byts[4 : 4+length]
+	return 4 + length, nil
+}
+
+// Marshal encodes the header.
+func (h QuantizationTable) Marshal(byts []byte) []byte {
+	byts = append(byts, h.MBZ)
+	byts = append(byts, h.Precision)
+	l := len(h.Tables)
+	byts = append(byts, []byte{byte(l >> 8), byte(l)}...)
+	byts = append(byts, h.Tables...)
+	return byts
+}