Abstract
During the last decade, multimedia streaming has experienced explosive growth. Adaptive video has become a necessity for meeting stringent QoS requirements in non-guaranteed IP networks. Since the user is the final point in the multimedia distribution chain, transmission rate must be adjusted to match the requirements set, the end-to-end effective bandwidth, and the capabilities of the terminals used to access the services offered. In addition, the concept of pervasive and ubiquitous computing has increased the need for rate adaptation so as to fulfill the restrictions posed by mobile terminals (e.g., phones and handhelds). The ultimate goal is the optimization of the subjective audio-visual quality.
Key Terms in this Chapter
Transcoding: The term in general refers to the conversion from one encoding scheme to another.
Real-Time Transport Protocol (RTP): Application layer protocol that is used for the transmission of multimedia files that need to be displayed in real-time (i.e., streaming applications) through IP-based networking platforms. UDP is usually the transport protocol when RTP packets are sent.
Moving Picture Experts Group (MPEG): ISO/ IEC working group for developing and standardizing audio/video coding formats. The list of relevant standards includes MPEG-1 (Video CD and MP3 audio format are based on MPEG-1), MPEG-2 (HDTV and DVDs), MPEG-4 (object-based multimedia representations available at a variety of bit rates), MPEG-7 (for multimedia description), and MPEG-21 (multimedia framework).
Real-Time Transport Control Protocol (RTCP): Protocol (complementary to RTP) that is used to convey feedback information to the sender of RTP packets, so as to provide the status of the receiver through reports regarding lost packets and the delay/jitter the stream is experiencing.
Discrete Cosine Transform (DCT): Transform used in signal and image processing applications. JPEG, MPEG, MJPEG, and DV are video and image formats based on DCT.
Encoding/Decoding: The term “encoding” refers to the process of transforming a raw/uncompressed image and/or video file into a compressed form, through exploitation of spatial-temporal redundancies. Decoding is the reverse process, i.e., the retrieval of the original files through the encoded ones.
Streaming: Term used to describe the transmission and reproduction of multimedia data. Transmitted data are viewed upon reception of the data packets the media content is encapsulated in. The term contradicts oldest multimedia applications of the download-andplay form.