MOV vs MP4 vs MKV vs AVI: Which Video Format Should You Use?
Video format confusion usually shows up at the worst possible moment — a file that won't upload, a clip that plays with no sound on one device but fine on another, an old recording that a current editor refuses to open. Most of that comes down to a handful of container formats that each made a different tradeoff, and knowing which one you're dealing with makes the fix obvious.
MP4: the safe, universal default
MP4 is the closest thing video has to a universal standard — recognized by essentially every device, browser, platform, and piece of editing software in common use. If you're not sure what format something needs, MP4 is almost always the right guess. It's also the most common target when converting from something less compatible, which is why the video converter defaults so often to MP4 as the destination format.
MOV: Apple's native format
MOV is what an iPhone or Mac saves video as by default, and within Apple's own ecosystem it works flawlessly. Step outside that ecosystem — a Windows PC with older software, certain upload forms, some non-Apple editing tools — and MOV support gets noticeably less consistent than MP4's. That's the entire reason MOV to MP4 exists as a dedicated conversion: it's specifically the fix for "this iPhone video won't open on my computer at work."
MKV: built for extras, at the cost of universal support
MKV is a flexible container designed to hold high-bitrate video alongside multiple audio tracks (useful for multiple languages) and multiple subtitle tracks, all in one file — which is exactly why it's a common choice for downloaded high-quality video releases. The tradeoff is that support across mobile devices, smart TVs, and various streaming boxes is less consistent than MP4's, so an MKV file that plays perfectly on a desktop media player might simply refuse to open on a phone or a smart TV. MKV to MP4 trades away MKV's embedded extras for that broader compatibility.
AVI: the format that time mostly passed by
AVI was a dominant format years ago, and it still turns up from older camcorders, legacy screen-recording software, and archived video collections. Modern devices and current software have largely moved on, so an old AVI file can be surprisingly difficult to open, edit, or share today compared to when it was created. AVI to MP4 is specifically built for exactly this: making decades-old footage usable on current hardware again.
When conversion is actually worth doing
If a video plays fine everywhere you need it to, there's no benefit to converting it — format alone doesn't affect quality one way or the other. Conversion earns its place when a specific destination rejects the current format outright, when you're combining clips from different sources that need to share one format before editing, or when you're trying to modernize an old archive so it stays usable on current devices. In all three cases, MP4 is almost always the destination worth converting to.
The video converter covers all of these conversions and more — MOV, AVI, MKV, WEBM, and GIF — in one tool, run entirely in your browser with no upload required. Once your video is in a compatible format, Compress Video is often the next useful step if file size still needs to come down; our guide to compressing video without ruining quality covers that in detail.