MPEG-2 Standard By Rigoberto Fernandez
MPEG Standards • MPEG (Moving Pictures Experts Group) is a group of people that meet under ISO (International Standards Organization) to generate standards for digital video and audio compression. In particular, they define a compressed bit stream, which implicitly defines a decompressor.
The following MPEG standards exist: • MPEG-1, a standard for storage and retrieval of moving pictures and audio on storage media. • MPEG-2, a standard for digital television. • MPEG-4, a standard for multimedia applications. • MPEG-7, a content representation standard for information searches.
MPEG-2 Video Compression The MPEG-2 video compression algorithm achieves very high rates of compression by exploiting the redundancy in video information. MPEG-2 removes both the temporal redundancy and spatial redundancy, which are present in motion video.
• Temporal redundancy arises when successive frames of video display images of the same scene. It is common for the content of the scene to remain fixed or to change only slightly between successive frames. • Spatial redundancy occurs because parts of the picture (called pels) are often replicated (with minor changes) within a single frame of video.
Video Stream Data Hierarchy
Picture Types • The MPEG standard specifically defines three types of frames. The picture type defines which prediction modes may be used to code each block. These three type of pictures are defined as follows: • Intra Pictures (I-Frames) • Predicted Pictures (P-Frames) • Bidirectional Predicted Pictures (B- Frames)
Profile and Levels A profile is a subset of algorithmic tools and a level identifies a set of constraints on parameter values (such as picture size or bit rate). The profiles and levels defined to date fit together such that a higher profile or level is superset of a lower one. A decoder, which supports a particular profile and level is only required to support the corresponding subset of algorithmic tools and set of parameter constraints.
Interlaced Video and Picture Structures An interlaced video sequence uses one of two picture structures: frame structure and field structure. The interlaced video sequence can switch between frame structures and field structures on picture-by-pictures basics. On the other hand, each picture in a progressive video sequence is a frame picture.
MPEG-2 Advance Audio Coding • It provides a low bitrate coding for multichannel audio. • In general there are five full bandwidth channels. • AAC basically makes use of the signal masking properties of the human ear in order to reduce the amount of data
Differences between MPEG-2 AAC and its predecessor ISO/MPEG Audio Layer-3 • • • Filter bank Temporal Noise Shaping TNS Bit-stream format Prediction Quantization
MPEG-2 standard features • Video compression which is backwards compatible with MPEG-1 • Full-screen interlaced and/or progressive video • Enhanced audio coding • Transport multiplexing • Other services