MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio and metadata such as subtitles and closed captioning without excessive quality loss, making video CDs, digital cable and satellite TV and digital audio broadcasting (DAB) possible as well as allowing for easy file-sharing of moving pictures for such uses as reference, archiving and transcription. MPEG-1 is used in a large number of products and technologies, most notably the MP3 audio format. MPEG-1 was developed by MPEG (Moving Pictures Experts Group) beginning in 1988 to address the need for standard video and audio formats and to build on the H.261 standard to get better quality through the use of more complex encoding methods.

In July 1990, before the first draft of the MPEG-1 standard had been completed, work began on a second standard, MPEG-2, intended to extend MPEG-1 technology to provide full broadcast-quality video at high bitrates and to address shortcomings of the original MPEG-1 standard, including an audio compression system limited to two channels (stereo), no standardized support for interlaced video with poor compression when used for interlaced video and only one standardized profile, which was unsuited for higher resolution video.

The MPEG-1 standard very strictly defines the bitstream and decoder function but does not define how MPEG-1 encoding is to be performed, although a reference implementation is provided in ISO/IEC-11172-5. This means that MPEG-1 coding efficiency can drastically vary depending on the encoder used and that newer encoders generally perform significantly better than their predecessors.

Most popular software for video playback includes MPEG-1 decoding in addition to any other supported formats. Virtually all digital audio devices can play back MPEG-1 Audio. Before the formulation of MPEG-2, many digital satellite/cable TV services used MPEG-1 exclusively. The widespread popularity of MPEG-2 with broadcasters means MPEG-1 can be played by most digital cable and satellite converter boxes and digital disc and tape players due to backwards compatibility.

MPEG-1 is the exclusive video and audio format used on Green Book CD-i, the first consumer digital video format, and on Video CD (VCD), still a very popular format around the world. The Super Video CD standard, based on VCD, uses MPEG-1 audio exclusively, as well as MPEG-2 video. Most DVD players also support Video CD and MP3 CD playback, which use MPEG-1.

The primary file extension for MPEG-1 or MPEG-2 audio and video compression is .mpg. The most common file extension for MPEG-1 Layer 3 audio is .mp3. An MP3 file is typically an uncontained stream of raw audio.