This book constitutes the refereed proceedings of the 4th International Conference on Multimedia Communications, Services and Security, MCSS 2011, held in Krakow, Poland, in June 2011.The 42 revised full papers presented were carefully reviewed and selected from numerous submissions. Topics addresses are such as audio-visual systems, service oriented architectures, multimedia in networks, multimedia content, quality management, multimedia services, watermarking, network measurement and performance evaluation, reliability, availability, serviceability of multimedia services, searching, multimedia surveillance and compound security, semantics of multimedia data and metadata information systems, authentication of multimedia content, interactive multimedia applications, observation systems, cybercrime-threats and counteracting, law aspects, cryptography and data protection, quantum cryptography, object tracking, video processing through cloud computing, multi-core parallel processing of audio and video, intelligent searching of multimedia content, biometric applications, and transcoding of video.