support decoding M-JPEG streams with any quantization (#566) (#583)

pkg/format/rtpmjpeg/header_quantization_table.go

@@ -7,7 +7,7 @@ import (
 type headerQuantizationTable struct {
 	MBZ       uint8
 	Precision uint8
-	Tables    []byte
+	Tables    [][]byte
 }
 
 func (h *headerQuantizationTable) unmarshal(byts []byte) (int, error) {
@@ -18,29 +18,42 @@ func (h *headerQuantizationTable) unmarshal(byts []byte) (int, error) {
 	h.MBZ = byts[0]
 	h.Precision = byts[1]
 	if h.Precision != 0 {
-		return 0, fmt.Errorf("Precision %d is not supported", h.Precision)
+		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)
+		return 0, fmt.Errorf("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]
+	tableCount := length / 64
+	h.Tables = make([][]byte, tableCount)
+	n := 0
+
+	for i := 0; i < tableCount; i++ {
+		h.Tables[i] = byts[4+n : 4+64+n]
+		n += 64
+	}
+
 	return 4 + length, nil
 }
 
 func (h headerQuantizationTable) marshal(byts []byte) []byte {
 	byts = append(byts, h.MBZ)
 	byts = append(byts, h.Precision)
-	l := len(h.Tables)
+
+	l := len(h.Tables) * 64
 	byts = append(byts, []byte{byte(l >> 8), byte(l)}...)
-	byts = append(byts, h.Tables...)
+
+	for i := 0; i < len(h.Tables); i++ {
+		byts = append(byts, h.Tables[i]...)
+	}
+
 	return byts
 }