MP4, MOV, MKV, AVI and WebM: What the Difference Actually Is

People treat MP4, MOV, MKV and AVI as different kinds of video. They are not, quite. They are different boxes, and what matters just as much is what has been put inside them. Getting this distinction straight explains most of the confusion around video files — including why a file that will not play in one app plays perfectly in another.

Containers and codecs

A video file has two layers.

The container is the file format itself — MP4, MOV, MKV, AVI, WebM. It defines how streams are packaged together, how timing information is stored, and what metadata can be attached. The container is what the file extension tells you.

The codecs are how the actual video and audio are compressed inside it: H.264, H.265, VP9 or AV1 for the picture; AAC, MP3, Opus or AC-3 for the sound. The extension tells you nothing about these.

This is why two MP4 files can behave completely differently. One holding H.264 video and AAC audio plays anywhere; one holding H.265 and AC-3 may refuse to open on older hardware. Same extension, different contents.

The containers you will actually meet

MP4 is the universal standard. Phones record it, cameras export it, streaming services deliver it, and every device plays it. If you have a choice, this is the one to have.

MOV is Apple's container, created for QuickTime. Technically it is closely related to MP4 — MP4 was derived from it — and modern MOV files usually hold the same H.264 and AAC that an MP4 would. iPhones record MOV, and it is well supported outside Apple's world these days.

MKV (Matroska) is an open container built for flexibility. It holds any codec, multiple audio tracks, multiple subtitle tracks and chapters, which is why rips and archival recordings use it. Media players handle it well; phones and smart TVs are less reliable.

AVI is Microsoft's format from 1992 and shows its age. It predates modern codecs and handles them awkwardly, with no proper support for variable frame rate or modern subtitles. You meet it in older archives and camcorder transfers.

WMV is Windows Media Video, the 2000s Windows standard. It typically holds Windows Media codecs that non-Windows software often cannot decode, which is why WMV files so often refuse to open on a Mac.

WebM is Google's open container for the web, holding VP9 or AV1 video with Opus or Vorbis audio. Browsers handle it natively; standalone players and devices frequently do not.

Why a file will not play

Almost always, the codec rather than the container is at fault. Your player recognises the box, opens it, and finds something it cannot decode — which typically produces audio with no picture, or an error mentioning a missing codec.

The usual culprits are H.265/HEVC on older hardware, AC-3 or DTS audio in a player without licensing for it, and Windows Media codecs anywhere outside Windows. Occasionally the container itself is the problem, as with MKV on a smart TV.

Why extraction works from all of them

Here is where the distinction becomes useful. Extracting audio does not care much which container you have. The process opens the box, finds the audio stream inside, decodes it, and re-encodes it as MP3. The wrapper is incidental.

That is why the video to MP3 tool accepts MP4, MOV, MKV, AVI, WMV, WebM, FLV, MPEG, 3GP and TS through the same path — and why a MOV from an iPhone and an MKV screen recording produce equally clean results. If your file happens to be an MP4, the dedicated MP4 to MP3 tool does the same thing with a narrower input list.

It also means extraction often works on files that will not play for you. A WMV whose video codec your Mac cannot decode still has a perfectly readable audio stream — which is frequently the reason people extract in the first place.

What audio is inside each

Worth knowing when picking a bitrate. MP4 and MOV nearly always carry AAC, typically 128 to 192 kbps. MKV varies enormously — AAC, AC-3, DTS, FLAC or Opus, depending on the source. AVI usually carries MP3 or older Windows Media Audio. WMV carries WMA. WebM carries Opus or Vorbis.

Since re-encoding cannot exceed the source, this tells you what you have to work with. Most videos sit around 128 kbps, which is why 192 kbps is a comfortable target and 320 kbps is usually wasted — the bitrate guide works through it.

The practical summary

The extension tells you the box, not the contents. Playback problems are usually codec problems, not container problems. Audio extraction works regardless of the container, and often works on files that will not play at all. And when you need one format that everything handles, MP4 with H.264 and AAC remains the safe answer.

To pull audio out of whatever you have, start with video to MP3, or MP4 to WAV if the result is heading into an editor. The step-by-step guide covers the process, and the batch guide covers doing it to a folder at a time.