The first time someone handed us a .MOV file that refused to play on their shop's Windows laptop, we wrote down the explanation we gave them. It turned into this guide.
Containers, codecs, and why this is confusing
Almost every video file is two things in a trench coat: a codec (the compression method that actually encodes the pictures and sound) and a container (the box that packs video, audio, subtitles and metadata into one file). The letters at the end of a filename — .mp4, .webm, .mov — name the container, not the codec. That is why two MP4 files can behave completely differently: they may carry different codecs inside.
You do not need to memorise codecs. You need to know which container works where.
The three you actually meet
- MP4 (H.264 inside) — the world's default. Plays on every phone, computer, smart TV, browser and social platform made in the last fifteen years. If you do not know what to pick, pick this.
- MOV — Apple's container. Beautiful quality, common from iPhones and professional cameras, perfectly playable on Macs. Windows machines and many web services handle it less gracefully, and files tend to run large.
- WebM — built for the web, efficient and open. Great for embedding in websites; weaker support in phone galleries, TV players and office software.
Choosing by destination
- Sending to a person (email, WhatsApp, Telegram): MP4. It must play on a device you cannot see.
- Uploading to a platform (YouTube, Instagram, TikTok): they all accept MP4 happily. Upload MP4 and stop thinking about it.
- Playing on an old office computer or smart TV: MP4, at a modest resolution.
- Embedding on your own website: WebM or MP4 — MP4 is the safe default here too.
Converting with the Video Converter
The Video Converter runs a real video encoder inside your own browser using WebAssembly — your file is processed on your device and never uploaded:
- Open the tool and pick your video (the free tier handles files up to 100 MB).
- Choose the output format and, if offered, the target resolution.
- Let it run. Real video encoding takes real time — minutes, not seconds — and the tab must stay open, because your computer is doing the work locally.
- Download the result and check it plays where you intend to send it.
The first conversion loads the encoding engine into your browser cache; afterwards it starts faster.
Two honest expectations
- Re-encoding always costs some quality. Each generation of encoding slightly softens the image. Convert from your original file, convert once, and keep the master untouched.
- File size depends on settings, not container alone. If the goal is a smaller file, you want the Video Compressor, which targets size directly — see our guide to sending videos on WhatsApp.
Format confusion is really a compatibility problem, and MP4 solves it about 95% of the time. Convert, verify, send.