It is critical for applications to obtain enough quality of service (QoS) from multimedia objects. Not only states but also QoS of objects are changed if methods are performed on the objects. The objects are required to be consistent with respect to state and QoS of objects in presence of multiple transactions issuing requests to the objects. We discuss new types of consistent and conflicting relations among methods with respect to QoS. We introduce two types of locking modes, serialization and mutually exclusive modes to synchronize concurrent accesses to objects based on the QoS relations. We also discuss how these lock modes conflict.