Three containers, three personalities. Here's the plain-English version — and how to switch between them in seconds.
Video files end in .mp4, .webm, .mov — and most people treat those letters as decoration. They're actually containers: wrappers that hold the video picture, the audio, and some metadata. The wrapper you pick decides where your video will play, how big it is, and who can open it. Here's what each of the big three is good at.
MP4 (usually with H.264 video and AAC audio inside) is the closest thing the video world has to a universal language. It plays on iPhones, Androids, Windows, Macs, smart TVs, browsers, game consoles — basically everything made in the last fifteen years. If you're sharing a video with other humans and you're not sure what they use, MP4 is the safe answer. It's also what TikTok, Instagram Reels and YouTube Shorts expect for uploads.
WebM is Google's open format, built for the web. With modern VP9 video inside, it can deliver the same visual quality as MP4 at a noticeably smaller file size — great for embedding video on a website where every kilobyte affects loading speed. The catch: support outside browsers is patchier. Many Apple devices and some desktop players needed years to catch up, and some video editors still dislike it. Use WebM when the destination is a web page; prefer MP4 when the destination is a person.
MOV is Apple's container — it's what iPhones produce when you hit record. Inside, it's very often the exact same H.264 video you'd find in an MP4, just in an Apple-flavored wrapper. That means MOV files sometimes confuse Windows software, older players and some web services for no good technical reason. If your iPhone video won't open somewhere, the container is the usual suspect, not the footage.
Does converting reduce quality?
Slightly, yes — converting re-encodes the picture, and every re-encode discards a little data. In practice, one conversion from a good original is visually indistinguishable. Just avoid converting back and forth repeatedly, and always keep the original file.
Which format gives the smallest file?
As a rule of thumb, WebM (VP9) beats MP4 (H.264) on size at equal quality, and both beat an unoptimized MOV from a phone. But the biggest wins come from lowering resolution and bitrate — see our compression guide — not from the container alone.
Why won't my .mov open on my friend's PC?
Almost certainly a container/codec support issue on their player, not a broken file. Convert it to MP4 and the problem disappears.