xsd validate chose based on parent value

Question

I have following xsd schema :-

 <xsd:element name="content-transaction">
<xsd:complexType>
  <xsd:sequence>
    <xsd:element name="ClientID" type="xsd:string"/>
    <xsd:element name="ContentTypeParent">
      <xsd:simpleType>
        <xsd:restriction base="xsd:positiveInteger">
          <xsd:minInclusive value="1"/>
          <xsd:maxInclusive value="3"/>
        </xsd:restriction>
      </xsd:simpleType>
    </xsd:element>
    <xsd:element name="Item" maxOccurs="unbounded">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="Active">
            <xsd:simpleType>
              <xsd:restriction base="xsd:positiveInteger">
                <xsd:minInclusive value="1"/>
              </xsd:restriction>
            </xsd:simpleType>
          </xsd:element>
          <xsd:choice>
            <xsd:element name="Images" type="ImagesType"></xsd:element>
            <xsd:element name="Audio" type="AudioType">
              <xsd:annotation>
                <xsd:documentation>based on Content Type Parent, Audio = 2</xsd:documentation>
              </xsd:annotation>
            </xsd:element>
            <xsd:element name="Video" type="VideoType">
              <xsd:annotation>
                <xsd:documentation>based on Content Type Parent Video = 3</xsd:documentation>
              </xsd:annotation>
            </xsd:element>
          </xsd:choice>
        </xsd:sequence>

      </xsd:complexType>
    </xsd:element>
  </xsd:sequence>
</xsd:complexType>

 <xsd:complexType name="ImagesType">
<xsd:sequence>
  <xsd:element name="DPI" minOccurs="0">
    <xsd:simpleType>
      <xsd:restriction base="xsd:positiveInteger">
        <xsd:maxInclusive value="1000000"/>
      </xsd:restriction>
    </xsd:simpleType>
  </xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="AudioType">
<xsd:sequence>
  <xsd:element name="UPC" minOccurs="0">
  </xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="VideoType">
<xsd:sequence>
  <xsd:element name="SeasonNum" minOccurs="0">
    <xsd:simpleType>
      <xsd:restriction base="xsd:positiveInteger">
        <xsd:maxInclusive value="100"/>
      </xsd:restriction>
    </xsd:simpleType>
  </xsd:element>
</xsd:sequence>
</xsd:complexType>

Now its validating any option from Image,Audio and Video. but I want it to validate according to ContentTypeParent for example if its 1 only Image tag should be present in xml file if its 2 then Audio and 3 for 'Video'. I am new in xsd and i have try but can't found any way to make it work.