How MPG Works
MPG (also written .mpeg) is the classic video file format carrying MPEG-1 or MPEG-2 video, the standards that powered VideoCD, DVD, and digital television. Where the broad "MPEG" name refers to a whole family of standards, an .mpg file specifically is one of these older program streams: a self-contained file that multiplexes MPEG video and audio together for playback. It is the on-disk format you actually get when content is encoded with those early MPEG generations.
The compression inside follows the foundational MPEG approach. It combines spatial coding, a block-based discrete cosine transform with quantization (the same idea JPEG uses on still images), with temporal coding that exploits redundancy between frames. Frames are organized into groups of pictures built from I-frames (complete, independently coded images), P-frames (predicted from earlier frames), and B-frames (predicted from both earlier and later frames). Storing full pictures only occasionally and describing the rest as changes is what gives MPG its compression.
This design was a milestone, MPEG-1 enabled VideoCD and the MP3 audio layer, while MPEG-2 became the backbone of DVD and broadcast TV for years, but by modern standards it is inefficient. An .mpg file is considerably larger than an H.264 MP4 of the same quality, because the codecs inside it predate the major efficiency gains of later generations.
Where MPG Came From and Where It Lives Now
MPG files are largely a legacy of the DVD and early digital video era. You meet them in old captured video, DVD-derived content, VideoCD files, and recordings from older cameras and TV capture devices that defaulted to MPEG-1/2. They remain broadly playable in most media players, since MPEG-1/2 decoding is mature and widespread, but they are no longer produced by modern workflows, which use H.264 in MP4 instead.
The practical step for old MPG files is to convert them to MP4. Because MP4 with H.264 is far more efficient, the same video becomes a much smaller file, and it gains the universal device and platform compatibility that the aging MPG format lacks. Converting also makes the content easier to edit and upload, since many modern tools and sites prefer MP4.
When You Encounter MPG
MPG turns up almost exclusively in older and DVD-derived video: archived recordings, ripped or authored DVD content, VideoCD files, and captures from legacy hardware. There is no reason to choose MPG for new video, since modern formats are smaller and better supported. For any MPG file you want to preserve or share, converting it to MP4 is the standard, future-proof move that shrinks the file and modernizes its compatibility.
Limitations
MPG's limitations are those of its codec generation. The MPEG-1/2 compression it carries is inefficient by modern standards, producing much larger files than H.264 for equivalent quality. It also lacks the rich multi-track, subtitle, and streaming features of MP4 and MKV, and it is purely a legacy delivery format with no role in new production. It stays widely playable, which is its one practical virtue, but for storage, sharing, or editing, MP4 is the clear upgrade.
