MPEG-1 is the earliest format specification in the family of MPEG formats. Because of its
low bit rate, MPEG-1 has been popular for online distribution and in formats such as Video
CD (VCD). DVDs can also store MPEG-1 video, though MPEG-2 is more commonly used.
Although the MPEG-1 standard actually allows high resolutions, almost all applications use
NTSC- or PAL-compatible image dimensions at quarter resolution or lower.
Common MPEG-1 formats include 320 x 240, 352 x 240 at 29.97 fps (NTSC), and
352 x 288 at 25 fps (PAL). Maximum data rates are often limited to around 1.5 Mbps.
MPEG-1 only supports progressive-scan video.
MPEG-1 supports three layers of audio compression, called MPEG-1 Layers 1, 2, and 3.
MPEG-1 Layer 2 audio is used in some formats such as HDV and DVD, but MPEG-1 Layer
3 (also known as MP3) is by far the most ubiquitous. In fact, MP3 audio compression
has become so popular that it is usually used independently of video.
MPEG-1 elementary stream files often have extensions such as .m1v and .m1a, for video
and audio, respectively.