MPEG-4 is an ISO/ IEC 14496 standard developed by MPEG in 1998 and adopted by ISO/IEC. The backward compatible version 2 of MPEG-4 was adopted in 2000. MPEG-4 deals with video, interactive audiovisual applications, and interactive multimedia.
The difference between MPEG-4 and MPEG-1 and -2
MPEG-4, unlike MPEG-1 and MPEG-2, does not specify a single compression scheme, but defines a collection of audio and video compression schemes. It forms a framework that supports the integration of arbitrary media objects, as well as the interaction between human users and the audiovisual world. In addition, MPEG-4 defines low- data-rate speech coding, audiovisual objects that can be individually compressed and assembled into audio sequences, multichannel sound, animation of virtual reality objects, frame insertion, and more.
With MPEG-4, a scene can be divided into audiovisual objects. The objects can be described separately using a special description language and can be changed and reassembled by the user through interaction. The composition of multimedia presentations can thus take place at the receiver. For this purpose, MPEG-4 defines a binary format for scene description, the Binary Format for Scene Description( BIFS), which is based on an extension of the Virtual Reality Modeling Language( VRML).
Profiles under MPEG-4
MPEG-4 has many different profiles such as the Visual Profiles, Audio Profiles, Graphics Profiles, Scene Graph Profiles, MPEG Profiles, and the Object Descriptive Profiles. With these profiles, graphic elements in the form of simple lines or complex polygons, solids and surfaces, 2D and 3D models, real, synthetic and video objects and different audio compressions such as Code Excited Linear Prediction( CELP) and Harmonic Vector Excitation( HVXC), Harmonic and Individual Line Plus Noise( HILN), TwinVQ and the AAC compression, Advanced Audio Coding ( AAC) are supported.
In MPEG-4, the generic interface between the application and the transport networks is the Delivery Multimedia Integration Framework( DMIF) with the DMIF interfaces to the network( DNI) and to the application( DAI)
The data rates of MPEG-4
The data rates of MPEG-4 are between 5 kbit/s and 4 Mbit/s for video, i.e. the same as for MPEG-1 and MPEG-2. In addition, MPEG-4 works with Scalable Video Coding( SVC) and can scale the video stream in the frame rate (Temporal), the display size (Spatial) and the display quality (Quality) between QCIF, the CIF display format, 4CIF up to high-definition television ( HDTV). This ensures adaptation to the corresponding end devices - cell phone, smartphone, notebook and television.
MPEG-4 audio compression uses several efficient coding schemes that are optimized specifically for speech, music, or synthetic sounds. These include AAC compression, Code Excited Linear Prediction (CELP) and Harmonic Vector Excitation (HVXC) for speech compression, and Harmonic and Individual Line Plus Noise (HILN) for music.