MPEG-1 Video Stream Layers
It is the international standard for audio/video digital compression. MPEG-1 is the most relevant for video at a low data rate (up to 1.5 Mbit/s) to be incorporated into multimedia. MPEG-1 is a standard in 5 parts, namely Systems, Video and Audio, Conformance Testing and Software Simulation. Though higher standards like MPEG-2, MPEG-3, and MPEG-4 have evolved in search of higher compression ratio, better video quality, effective communication and technological degradation.
It doesn’t actually define a compression algorithm. It also defines a datastream syntax and a decomposer. The data stream architecture is based on a sequence of frames, each of which contains the data needed to create a single displayed image. There are four different kinds of frames, depending on how each image is to be decoded:
I-frames: It stands for Intra-coded frames. These images are self-contained, they are coded without any reference to the other images. These frames are purely spatially compressed using a transform coding method similar to JPEG. The compression ratio for I-frames is the lowest within MPEG. An I-frame must exist at the start of any video stream and also at any random access entry point in the stream.
P-frames: It stands for Predictive-coded frames. These images are composed of images resulting from the removal of temporal redundancy between successive frames. These frames are coded by a forward predictive coding method. The targeted macroblocks are predicted from most similar reference macroblocks in the preceding I or P-frame.
B-frames: It stands for Bi-directionally predictive-coded frames. They are coded by interpolating between two macroblocks one from forwarding prediction and the other from backward prediction.
D-frames: It stands for DC coded frames. They are intra-frame coded and used for fast forward or fast rewind modes.