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Our free online video converter supports a wide range of video formats including MP4, AVI, MKV, MOV, WebM, WMV, FLV, 3GP, and more. All conversions are performed directly in your browser using FFmpeg WebAssembly technology, ensuring your files remain private and secure.
Whether you need to convert videos for a presentation, optimize for web streaming, or prepare content for mobile devices, our tool provides fast and reliable conversions with high-quality output.
One of the most common points of confusion with video files is the difference between a container format and a codec. They solve different problems, and understanding the distinction will help you make better choices when converting video.
A container (like MP4, MKV, or WebM) is the "wrapper" that holds everything together. Think of it like a shipping box: it doesn't change what's inside, but it determines how the contents are organized and what shipping services will accept it. A container holds the video stream, the audio stream, subtitles, metadata (like the title and chapter markers), and sometimes even thumbnail images.
A codec (like H.264, H.265, or VP9) is the compression algorithm that actually encodes the video data. This is what determines the visual quality and file size. The same codec can live inside different containers. For example, H.264 video works inside MP4, MKV, and MOV files. The container is the box; the codec is how the contents were packed.
When you "convert a video," you might be changing the container (fast, no quality loss), the codec (slow, may affect quality), or both. If you just need a different file extension for compatibility, a container swap is quick and lossless. If you need a smaller file size, you'll need to re-encode with a more efficient codec.
| Format | Best For | Codec Support | Browser Support | File Size |
|---|---|---|---|---|
| MP4 | General use, sharing, social media | H.264, H.265, AAC | All major browsers | Medium |
| MKV | Archiving, movies with multiple audio/subtitle tracks | Nearly all codecs | Limited (requires plugins or players) | Varies (depends on codec) |
| WebM | Web embedding, HTML5 video | VP8, VP9, AV1, Opus | Chrome, Firefox, Edge | Small to medium |
| AVI | Legacy compatibility, older systems | DivX, Xvid, MPEG-4 | None natively | Large (often uncompressed or lightly compressed) |
| MOV | Apple ecosystem, video editing | H.264, H.265, ProRes | Safari; limited elsewhere | Medium to large |
| WMV | Windows-only workflows, legacy media | WMV9, VC-1 | None natively | Medium |
MP4 is the safe default. If you're not sure which format to use, MP4 with H.264 video and AAC audio will play on virtually every device, browser, and platform made in the last 15 years. It's the format that social media platforms, messaging apps, and websites all expect.
MKV is ideal when you need to keep multiple audio tracks (like different languages) or subtitle tracks in a single file. It supports practically every codec in existence. The downside is that most web browsers and mobile devices won't play it natively, so it's best for media you'll watch through a desktop player like VLC.
WebM is purpose-built for the web. If you're embedding video on a website and want smaller file sizes without sacrificing quality, WebM with VP9 is an excellent choice. It's an open format backed by Google and supported in Chrome, Firefox, and Edge.
MOV is Apple's native format. If you're working in Final Cut Pro, iMovie, or other Apple editing tools, MOV preserves the highest quality. For sharing outside the Apple ecosystem, convert to MP4.
AVI and WMV are legacy formats. You'll mostly encounter them on older files. They work fine, but there's rarely a reason to convert to them today unless you're dealing with older software that requires them.
The codec you choose has the biggest impact on two things you care about most: how your video looks and how large the file is. Newer codecs are better at compressing video (smaller files at the same quality), but they take longer to encode and may not be supported on older devices.
The workhorse of video. H.264 has been the standard since the mid-2000s and is supported by essentially everything: browsers, phones, smart TVs, game consoles, drones, security cameras. Encoding is fast because hardware acceleration is universal. The tradeoff is that it produces larger files than newer codecs at the same quality level. If compatibility matters more than file size, H.264 is your codec.
The successor to H.264, designed to deliver the same visual quality at roughly 50% of the file size. That's a dramatic improvement, especially for 4K content where file sizes balloon quickly. The catch: encoding is significantly slower, hardware support is less universal (though most devices made after 2017 handle it fine), and there are licensing complexities that have slowed adoption on the web. Great for archiving and personal media libraries.
Google's open-source answer to H.265. VP9 achieves comparable compression efficiency to HEVC but is royalty-free, which is why YouTube uses it for virtually all of its video. It has strong browser support (Chrome, Firefox, Edge) and good hardware decoding on modern devices. If you're producing video for the web and want small files without compatibility headaches, VP9 in a WebM container is a strong choice.
The newest and most efficient codec, developed by the Alliance for Open Media (Amazon, Apple, Google, Meta, Microsoft, Netflix, and others). AV1 achieves roughly 30% better compression than H.265 and VP9, and it's royalty-free. The major downside is that encoding is extremely slow without dedicated hardware, and hardware decoding support is still rolling out (it requires newer GPUs and chips). AV1 is the future, but H.264 and VP9 are the present.
To put the differences in perspective, here's roughly what you'd see encoding the same 10-minute 1080p video clip:
These are approximate figures for a typical clip at medium bitrate settings. Actual sizes vary based on content complexity, resolution, and encoding settings.
Modern CPUs and GPUs include dedicated circuits for encoding and decoding video, which is dramatically faster than doing it in software. H.264 hardware acceleration is available on virtually every device. H.265 hardware support is common on devices from roughly 2017 onward. VP9 decoding is hardware-accelerated on many modern GPUs, but encoding is usually software-only. AV1 hardware support is arriving in the latest generation of GPUs (NVIDIA RTX 40-series, Intel Arc, Apple M3 and later).
Since our converter runs in your browser using WebAssembly, it uses software encoding rather than hardware acceleration. This means conversions may take longer than a native desktop application, but your files never leave your computer.
Not sure which format to convert to? Here are the most common situations and the best approach for each.
Convert to MP4 with H.264. Every social platform (Instagram, Twitter/X, Facebook, TikTok, LinkedIn) accepts MP4. They'll re-encode it on upload anyway, so there's no benefit to using a fancier codec. Keep the resolution at 1080p or lower for fastest upload and processing times.
Use MP4 or MKV with H.265. You'll get files roughly half the size of H.264 at the same visual quality. This is perfect for building a personal media library or archiving footage. If the device you're playing on supports H.265 (most modern devices do), there's no downside.
Use WebM with VP9 for the best balance of quality, file size, and browser compatibility. For maximum compatibility across all browsers (including Safari), provide an MP4 fallback using the HTML <video> element's multiple source feature.
Convert to MP4 with H.264. This is almost always a container or codec compatibility issue. MP4 + H.264 is the most universally supported combination and will play on virtually any device made in the last decade.
Convert the container to MP4. If the MKV already contains H.264 video, this can be done quickly by re-wrapping without re-encoding (called "remuxing"), which preserves the original quality. The recipient will be able to open it on any device without installing special software.
This depends on your editing software. MOV is preferred for Final Cut Pro and Apple workflows. MP4 works well with Adobe Premiere, DaVinci Resolve, and most other editors. Avoid heavily compressed codecs for editing source footage -- your editor will have to decompress every frame, which slows down playback and scrubbing.
It depends on what you're converting. If you're only changing the container format (like MKV to MP4) without re-encoding the video stream, there is zero quality loss. The video data stays identical; only the wrapper changes. However, if you re-encode to a different codec or a lower bitrate, some quality loss is inevitable. Video compression is "lossy," meaning each round of encoding discards some information. The loss is usually negligible with modern codecs at reasonable settings, but converting the same file repeatedly (like photocopying a photocopy) will visibly degrade quality over time.
A container (MP4, MKV, WebM) is the file format that organizes and stores the video, audio, and metadata streams. A codec (H.264, H.265, VP9) is the algorithm that compresses and decompresses the actual video data. A single container can hold video encoded with different codecs. For example, an MP4 file might contain H.264 video, or it might contain H.265 video. The container determines compatibility with players and platforms; the codec determines quality and file size.
The format (container) itself doesn't determine quality -- the codec and encoding settings do. A poorly encoded MP4 will look worse than a well-encoded WebM. That said, for the best quality-to-size ratio with current technology, use H.265 or VP9. If you need the absolute best and have time for slow encoding, AV1 is the most efficient codec available. For raw, uncompressed quality (like in professional editing), formats like ProRes in MOV are used, but they produce enormous files.
Our converter uses FFmpeg compiled to WebAssembly (WASM), which lets the powerful FFmpeg video processing library run directly inside your web browser. When you upload a file, it stays on your computer -- the video data is processed locally using your CPU, never sent to any server. This approach is slower than a native desktop application (since WebAssembly can't access GPU hardware acceleration), but it means your files remain completely private. No upload, no server processing, no data retention.
With our tool, yes. Because the conversion happens entirely in your browser, your video files are never uploaded to a remote server. This is fundamentally different from most online converters, which require you to upload your file, process it on their servers, and then download the result. Those services do have access to your files. With browser-based conversion, the video never leaves your device, so there's no privacy risk and no upload wait time.
File size is primarily determined by the codec and the bitrate setting. If you convert from a highly compressed codec (like H.265) to an older one (like H.264 or MPEG-4), the output file will likely be larger because older codecs are less efficient. Conversely, converting from an older codec to a newer one may shrink the file. The resolution and duration also matter: a 4K video will always be larger than a 1080p version of the same clip. If your converted file is unexpectedly large, check whether the output codec is less efficient than the source.