What is an MPEG file?

MPEG is a container: a wrapper that holds streams encoded by something else. It is used for broadcast and archiving.

The extension is .mpeg, and the full name is MPEG Video. Both matter less than what the file can hold, which is what the rest of this page is about.

MPEG published it in 1993. The specification is ISO/IEC 11172.

A format that has been readable for that long is a format worth trusting with something you want back in ten years.

It is published in full, so anyone can implement it from the document rather than by inspection, which is why it turns up in so many programs and why files written twenty years ago still open. A published specification is not the same thing as a royalty-free one: where a format wraps a codec, the patent licensing is a separate question the standard does not settle.

It still opens everywhere and is still written by older tools, but nothing new is being built around it. Convert what you mean to keep, and do not choose it for something starting today.

It usually holds MPEG-1 and MPEG-2. This is the distinction behind most "why will this not play" questions: two files with the same extension can contain entirely different encodings, and a player that refuses one may be perfectly happy with the other.

It also explains why changing container is often fast and lossless while changing codec is neither. Moving the same stream into a different box rewrites the box; re-encoding rewrites the picture.

MPEG can hold a layout that lets it start playing before it has finished arriving.

That matters mostly when converting: whatever the target cannot hold is dropped, usually without a warning.

VLC and FFmpeg read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

MPEG is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.

The recurring complaints: the files are large for what they contain.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

MPEG is the Moving Picture Experts Group, the standards committee that has defined most video and audio compression since 1988. Its output includes MP3, MP4, H.264, H.265 and AAC. So "an MPEG file" is ambiguous in a way that "a PNG file" is not.

In practice a file named `.mpg` or `.mpeg` is almost always one of two specific things: MPEG-1 video from the 1990s, or MPEG-2 video from DVDs, camcorders and digital broadcast. Everything below is about those two, because that is what people are actually holding.

MPEG-1 was finalised in 1993 to fit video onto a CD — 352 by 240 pixels at about 1.5 megabits per second, which was the achievable target at the time. Video CDs used it, early digital cameras recorded it, and the web served it before anything better existed.

Its third audio layer was specified in the same standard and became MP3. That is the one part of MPEG-1 still in daily use thirty years later, while the video half is now purely something to convert away from.

MPEG-2 arrived in 1995 and became the compression behind DVD-Video, digital television broadcast, and the DVD-based camcorders sold through the 2000s. A commercial DVD is MPEG-2 video in a program stream, and a recording from a set-top box very likely is too.

It is efficient for its age and hopeless by current standards. The same footage in H.264 is roughly half the size at the same quality, and in H.265 smaller again. That is the whole practical case for converting: nothing is wrong with the picture, the file is simply several times larger than it needs to be.

MPEG-2 travels two ways and the difference explains a lot. A program stream — the `.mpg` on a DVD — assumes storage is reliable and packs data efficiently. A transport stream, usually `.ts` or `.m2ts`, assumes it is not, and repeats synchronisation information constantly so a receiver can join partway and recover from errors.

That is why a recording from broadcast television or a Blu-ray is a transport stream: it was designed to be picked up mid-flight. It also means such a file can be slightly larger than its content needs, and can contain several programmes at once, which is why a recording sometimes plays the wrong channel.

Video from this era is frequently interlaced: each frame is two fields, one holding the odd lines and one the even, captured a fiftieth of a second apart on PAL and a sixtieth on NTSC. Televisions of the time drew it that way and it looked right.

On any modern screen it does not. Fast movement shows horizontal comb teeth along moving edges, because two moments in time are being displayed at once. This is the most recognisable sign of an MPEG-2 source, and it needs deinterlacing during conversion rather than afterwards — once both fields are flattened into one frame, the information to separate them is gone.

No subtitle track in the file — DVD subtitles live in a separate stream the container references, and they rarely survive extraction. No chapters in the video file itself; those belong to the DVD structure around it. No orientation flag, and no place for the metadata a modern camera writes.

Ripping a DVD to a single `.mpg` therefore loses the menus, the chapter marks and the subtitles even though the picture and sound arrive intact. If those matter, MKV is the container that holds them, which is a large part of why DVD archiving settled on it.

MPEG-2 was covered by a large patent pool and every DVD player, television and encoder carried a licence fee. Those patents expired around 2018, so the format is now free to use — and by then H.264 had replaced it everywhere and the point was moot.

The licensing history explains why free software handled MPEG-2 awkwardly for two decades and why it suddenly stopped being a problem. It is a fair illustration of how these formats age: by the time the legal obstacle cleared, the technical case had gone.

DVDs ripped to a hard drive. Camcorders that recorded to mini-DVD or hard disk through the 2000s. Recordings from a digital television tuner or set-top box. Video CDs, occasionally. Old digital cameras with a video mode. And archives assembled when MPEG-2 was simply what video was.

As with AVI, that means the file is usually old and often irreplaceable, and the value is in the footage rather than the format. Convert for watching; keep the original if it is the only copy of something.

H.264 in MP4 is the destination: it plays on everything, streams over a network, and will typically produce a file half the size at the same visible quality. Ask for deinterlacing if the source is interlaced, which anything from a DVD or a broadcast recording almost certainly is.

Do not be frugal with the quality setting. The source has already been through one generation of a weak codec, and the second pass should be generous enough to be invisible. A file at two-thirds the size instead of half but with no visible artefacts is the better outcome for footage that cannot be recaptured.