How to Convert MKV, AVI and Other Video Formats
Convert between MP4, MOV, MKV, WebM, AVI and FLV in your browser — what each format is for, and when a file can be repackaged in seconds without re-encoding.
3 min read ·
To change a video's format, open the Video Format Converter, add the video, choose what to Convert to — MP4, MOV, MKV, WebM, AVI or FLV — and press Convert. When the video already uses codecs the new format can hold, it's repackaged in seconds without any quality loss; otherwise it's converted with the codecs that format is known for.
Convert a video step by step
- Open the Video Format Converter.
- Add the video — MKV, AVI, MOV, WebM, FLV, WMV, 3GP, MTS and more — or paste a direct link to one.
- Choose the format under Convert to. A note shows which codecs it uses.
- Choose the Quality (used if re-encoding is needed): High, Standard or Smaller file.
- Press Convert to …. The result says whether the file was repackaged or converted. Download it.
Which format should I choose?
| Format | Inside | Use it for |
|---|---|---|
| MP4 | H.264 + AAC | Almost everything: phones, browsers, social sites, TVs |
| MOV | H.264 + AAC | Apple apps (iMovie, Final Cut, QuickTime) and editors |
| MKV | H.264 + AAC | Media players such as VLC, Plex and Kodi |
| WebM | VP8 + Vorbis | Embedding on websites with open formats |
| AVI | MPEG-4 (Xvid) + MP3 | Old DVD players, TVs and software |
| FLV | H.264 + AAC | Legacy Flash-based systems that still require it |
When in doubt, choose MP4.
Containers vs codecs (why some conversions take seconds)
A video file is a container (MP4, MKV, MOV…) holding streams compressed with a codec (H.264, HEVC, VP9…). Many containers can hold the same codec. So converting an MKV with H.264 inside to MP4 just moves the same streams into a new box — "repackaging" — which is lossless and nearly instant. Converting to a format that needs a different codec (MKV with HEVC → AVI, say) means re-encoding every frame, which takes longer.
Common conversions
- MKV to MP4 — usually repackaged in seconds (MKV downloads often contain H.264).
- AVI to MP4 — converted; old AVI codecs (DivX, Xvid) become H.264.
- MP4 to MOV — repackaged for Apple apps.
- MP4 to WebM — converted to VP8; this is the slowest conversion.
- WMV, 3GP, MTS to MP4 — converted; old phone and camcorder files become modern MP4s.
For the common "anything to MP4" job, Convert to MP4 is the same engine with one choice fewer.
What do websites and apps want?
Nearly every upload form — YouTube, Facebook, Instagram, TikTok, LinkedIn, Vimeo — prefers MP4 with H.264 and AAC. When a site rejects a file, converting it to MP4 is the first thing to try.
Subtitles and extra tracks
The converter keeps the main video and the first sound track. Extra audio tracks (other languages) and embedded subtitles from MKV files aren't carried over.
Only need the sound?
To turn a video into MP3, M4A or WAV, use Extract Audio; to convert between audio formats, the Audio Converter.
Privacy
Everything runs in your browser using ffmpeg (WebAssembly). Your videos aren't uploaded, and there's no watermark.
Frequently asked questions
Is the quality reduced?
Not when repackaging. When converting, High is visually identical; Smaller file trades a little detail for size.
Why did my MKV convert so fast?
It was repackaged: the video inside was already H.264, so nothing needed re-encoding.
Can I make the file smaller at the same time?
Choose Smaller file, or compress afterwards with Compress Video, which can also lower the resolution.