First: a container is not a codec
Almost every video-format mistake starts here. The file extension you see — .mp4, .mov, .mkv, .webm — is the container: the box that holds the video, audio, and subtitle streams. What actually determines file size and quality is the codec inside — H.264, H.265/HEVC, VP9, or AV1.
That’s why two .mp4files can be wildly different sizes, and why “convert my MOV to MP4” is often nearly lossless: if both use H.264, you’re just repackaging the same video into a more compatible box. When file size is the goal, the codec matters more than the container.
The 6 formats you need to know
MP4: the universal default
If you’re not sure what to use, use MP4 with H.264. It plays on every modern phone, browser, smart TV, editor, and social platform, and it compresses well. For 95% of people uploading, sharing, or storing a normal video, MP4 is the correct answer — and it’s what YouTube, Instagram, and TikTok all expect at upload.
Coming from another format? MOV to MP4 · MKV to MP4 · AVI to MP4 · WebM to MP4
MOV: great for editing, awkward for sharing
MOV is Apple’s QuickTime container. Your iPhone records in it, and it’s the format of choice for editing — especially ProRes masters, which keep near-original quality for colour grading and post-production. The catch is sharing: Windows machines and many web platforms don’t handle MOV cleanly, and ProRes files are enormous.
The practical workflow: edit in MOV, then export or convert to MP4 for delivery. Convert MOV to MP4, or go the other way with MP4 to MOV for your editor.
MKV: built for media libraries, not for playback anywhere
MKV (Matroska) is an open container that can bundle multiple audio tracks, subtitle languages, and chapters into one file — which is exactly why movie and TV rips use it. That richness is also its weakness: browsers, phones, and smart TVs mostly refuse to play MKV. VLC and Plex handle it on the desktop, but to watch a .mkv on a phone or TV, convert it first.
Convert MKV to MP4 for universal playback, or MP4 to MKVif you’re building a media library.
WebM: the smallest option for the web
WebM uses the open, royalty-free VP9 and AV1 codecs and is designed for HTML5 video. For background loops, hero videos, and inline clips, WebM files are typically 30–50% smaller than an equivalent H.264 MP4 — a real Core Web Vitals win. Every modern browser plays it. The usual pattern is to serve WebM with an MP4 fallback in the <video> tag so older devices still get a working file.
Convert MP4 to WebM for your site, or WebM to MP4 for sharing and editing.
AVI and GIF: mostly legacy
AVIis an old Microsoft container. It still turns up in archives and some camera exports, but it uses dated codecs and produces very large files — convert it to MP4 for modern use and to reclaim disk space.
GIFisn’t really video — it’s a sequence of images with no audio, capped at 256 colours, and shockingly large for anything more than a couple of seconds. For a short silent loop, a muted MP4 or WebM looks better and is a fraction of the size. Genuinely need a GIF (for a chat app or email)? Convert MP4 to GIF or MOV to GIF.
File size in practice: a real comparison
Same clip (1080p, 1 minute, moderate motion), packaged in different formats and codecs. Exact numbers depend on bitrate, but the relationships hold:
Convert any video format — free, in your browser
FormatDrop runs entirely in your browser. Your files never leave your device.
What is the best video format?↓
For sharing and compatibility, MP4 with the H.264 codec is the best all-round video format — it plays on virtually every phone, browser, TV, and editor. For the smallest files on a website, WebM (VP9 or AV1) is better and is natively supported by modern browsers. Use MOV for editing on Apple devices and MKV for archiving media with multiple audio and subtitle tracks.
What is the difference between MP4 and MOV?↓
Both are container formats that usually hold H.264 video. MOV is Apple's QuickTime format — iPhones record in MOV and it's ideal for editing (including ProRes). MP4 is the universal standard that plays everywhere. If a MOV file won't open on Windows or upload to a platform, convert it to MP4 — the video quality is unchanged because both commonly use the same codec.
Why won't my MKV file play?↓
MKV (Matroska) is an open container often used for movies and TV because it can hold multiple audio tracks and subtitles in one file. The trade-off is compatibility: most web browsers, phones, and smart TVs won't play MKV natively. Desktop players like VLC and media servers like Plex handle it, but for a phone or TV, convert MKV to MP4.
MP4 or WebM for a website?↓
WebM (VP9/AV1) produces smaller files and is open and royalty-free, which makes it ideal for HTML5 background and inline video. MP4 (H.264) has broader compatibility. The standard approach is to serve WebM with an MP4 fallback in the <video> tag so every browser gets a working, efficient file.
What is the difference between a container and a codec?↓
The container (.mp4, .mov, .mkv, .webm) is the box that holds the video, audio, and subtitle streams. The codec (H.264, H.265/HEVC, VP9, AV1) is how the video itself is compressed and is what actually determines file size and quality. Two .mp4 files can differ hugely in size depending on the codec inside. When file size matters, the codec matters more than the container.
Does converting a video reduce its quality?↓
Re-encoding video is lossy, but at a sensible bitrate the difference is imperceptible. Changing only the container (for example MOV to MP4 when both use H.264) can often be near-lossless. Keep the original resolution and a high bitrate to preserve quality when converting.