The possibility of storing TV signals (625- and 525-line systems) was also pursued, and their compatibility with work stations and personal computers was examined. For this reason MPEG-1 is based on progressively scanned images and does not recognize interlacing. Interlaced sources must be converted to a non-interlaced format before coding. The expected subjective quality of MPEG-1 was comparable to that of the competing analog technology at that time, i.e., video cassette recorder (VCR). Visualization features such as image freezing, fast forward, fast reverse, slow forward, and random access were also required for MPEG-1. It should be noted here that efficient coding and operational flexibility are usually conflicting requirements. The random search feature, for example, requires the insertion of regular images between frames. Those images do not explore the temporal redundancy present in the video signal, and so contribute to a lower compression ratio or a higher bit rate at the output of the coder.
The MPEG-1 standard did not include either the coder design or the decoder design. Manufacturers had freedom to adopt algorithms and to optimize them in order to achieve efficiency and functionality.