MPEG Is a Family, Not a Single Format
The most common confusion about MPEG is treating it as one format. In reality, MPEG is the Moving Picture Experts Group, the standards committee that has defined the most important video and audio compression technologies of the last thirty years. The name covers a whole family: MPEG-1, MPEG-2, MPEG-4, and the codecs and containers within them. When you see an .mpeg or .mpg file, you are usually looking at MPEG-1 or MPEG-2 video, but the MPEG name reaches far wider than those file extensions.
The core compression ideas MPEG introduced still power video today. MPEG-1 and MPEG-2 achieve their efficiency through a combination of block-based DCT (the same mathematical transform JPEG uses on images) and motion compensation, encoding most frames as predictions of nearby frames rather than as complete pictures. Frames are organized into I-frames (independently coded, a full picture), P-frames (predicted from previous frames), and B-frames (predicted from both past and future frames). This I/P/B structure, storing real images only occasionally and describing everything else as changes, is the foundation of nearly all modern video compression.
Each MPEG generation pushed this further. MPEG-1 brought VideoCD and, crucially, MP3 audio (MPEG-1 Audio Layer III). MPEG-2 powered DVD and digital television broadcasting for a generation. MPEG-4 introduced the modern era, including the H.264 (AVC) codec and the MP4 container that dominate video today. So the MPEG family is not a relic; it is the lineage that leads directly to the formats everyone uses now.
MPEG Files vs MPEG the Standard
It helps to separate two meanings. As a standards family, "MPEG" describes the technologies behind MP3, DVD, digital TV, H.264, and MP4, an enormous footprint across audio and video. As a file format, an .mpg or .mpeg file specifically is typically older MPEG-1 or MPEG-2 video, the kind found on VideoCDs, DVDs, and broadcast captures. So a modern MP4 is technically part of the MPEG family (MPEG-4) even though we do not call it an "MPEG file," while a 1990s .mpg is a direct, older MPEG-1/2 file.
When You Encounter MPEG Files
You meet actual .mpg/.mpeg files mainly in older video, DVD-derived content, and broadcast or VideoCD captures. These MPEG-1/MPEG-2 files play in most media players but are larger and less efficient than modern H.264 video. If you want to store or share them efficiently, converting them to MP4 (which is itself MPEG-4) keeps the video while shrinking the file and improving compatibility with current devices and platforms. For new video, you would use MP4 directly rather than the older MPEG file formats.
Limitations
The older MPEG file formats (MPEG-1/MPEG-2) have clear limits today: they are less efficient than modern codecs, so files are larger for the same quality, and they lack the rich multi-track and streaming features of MP4 and MKV. They remain widely playable, but they are legacy delivery formats rather than something to choose for new work. The broader MPEG family, by contrast, is anything but obsolete, its newer members (H.264, MP4, and beyond) are exactly what modern video runs on.
