Video Converter Online
A video file is a container holding separately encoded video and audio tracks, and converting between MP4, WebM, MKV, MOV and AVI is really about matching the codec inside to whatever device or platform needs to play it.
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Format reference
About this converter
The extension you see is a container format — a box that holds a video stream, an audio stream and metadata like subtitles or chapters — and the container is not the same thing as the codec doing the actual compression. MP4 usually carries H.264 or H.265 video with AAC audio; WebM carries VP8, VP9 or AV1 for royalty-free web delivery; MKV is the most permissive container, happily holding almost any codec combination plus multiple audio tracks and soft subtitles at once.
Re-encoding video is lossy and computationally expensive, unlike a simple remux. A remux repackages the same compressed streams into a different container in seconds, with zero quality change, and works whenever the target container already supports the codec inside — MKV to MP4 with H.264 video, for instance. A genuine re-encode decodes the video to raw frames and compresses again with a new codec or bitrate, which takes real time and always loses a little quality, more each time it happens.
Compatibility, not preference, drives most conversions here. MOV from an iPhone plays everywhere on Apple hardware but confuses some Windows software; AVI files from older downloads often carry codecs, like DivX, that modern players no longer bundle; MKV's rich feature set makes it a poor fit for phones and smart TVs that expect a plain MP4. Converting to MP4 with H.264 remains the closest thing to a universal format.
Frequently asked questions
- Which video format plays on the most devices?
- MP4 with H.264 video and AAC audio. Phones, smart TVs, browsers, game consoles and every major editing program decode it without extra codecs, which is why it is the default choice when you need a file to simply work everywhere.
- Does converting a video lose quality?
- A remux — repackaging the same compressed streams into a new container — loses nothing at all. A genuine re-encode to a different codec or bitrate always discards some information, though at a reasonably high bitrate the loss is usually invisible to the eye on a single pass.
- What is the difference between a container and a codec?
- The container (MP4, MKV, WebM) is the file format that packages video, audio and metadata together. The codec (H.264, H.265, VP9, AV1) is the compression method used inside it. The same codec can live in several containers, and the same container can hold several different codecs.
- Why won't my MKV file play on my smart TV or phone?
- Many consumer devices only decode a narrow set of codecs wrapped in MP4, while MKV often carries less common codecs, multiple audio tracks or subtitle formats those devices were never built to read. Converting to MP4 with H.264 video and AAC audio resolves the vast majority of these cases.
- Can I extract just the audio from a video file?
- Yes — converting a video to MP3, WAV or another audio format keeps only the soundtrack and discards the video stream entirely. This is the standard way to pull a podcast, lecture recording or music track out of a downloaded video.
- Why is my converted video file larger or smaller than the original?
- File size depends on the codec's efficiency and the bitrate chosen, not on the container. Converting from an older, less efficient codec to a modern one like H.265 or AV1 at the same visual quality typically shrinks the file; converting to a less efficient codec, or raising the bitrate, grows it.