MPEG-1 is a set of audio and video compression standards. MPEG-1 video compression, defined in ISO/IEC-11172-2 was heavily influenced by H.261.

MPEG-1 was primarily developed for use in the Video CD, the predecessor to the DVD. Typical resolutions used are Standard Interchange Format (352×240, 352×288 or 320×240) at a bit rate of 1.5 Mbps.

In MPEG-1, the image is divided into macroblocks consisting of a 16×16 array of luma samples and an 8×8 array of chroma samples just like in H.261. Three types of frames are defined. I-Frames consist entirely of intra-coded macroblocks which do not depend on previous frames. I-Frames are often called Key Frames and provide random access points within a video stream. P-Frames consist of macroblocks predicted from a previous I-Frame or other P-Frames. B-Frames consist of macroblocks which are predicted from a previous and a future I-Frame or P-Frame. MPEG-1 also uses D-Frames which only use the DC component of the DCT transform and were used for rapidly scanning through a video sequence. D-Frames have not been used in later compression algorithms.

The sequence of video images is broken into a Group of Pictures (GOP). Each GOP begins with an I-Frame followed by P-Frames and B-Frames. The next I-Frame marks the beginning of the next GOP. A typical GOP might be: IBBPBBPBBPBB(I). Both P-Frames and B-frames use Motion Vectors to account for macroblock motion between the actual and reference images. The Discrete Cosine transform (DCT) is then used on the five 8×8 blocks within each macroblock of the predicted image. Scalar quantization is used on the transform coefficients and Variable Length Coding (also called Entropy Coding) is used to remove statistical redundancy in the resulting values.