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Zero-Upload Browser Utility

Video Converter

Use this online video converter to transcode MP4, WebM, MKV, MOV, AVI, GIF, and audio-only MP3/AAC/Opus locally in your browser via FFmpeg WebAssembly.

Interactive Tool Workspace

Loading local in-browser WebAssembly engine & hardware cryptographic sandbox...

iPhones record in .mov, OBS Studio defaults to .mkv so crashes do not corrupt recordings, and web captures save as .webm - yet half the video editors, smart TVs, and social platforms only accept standard .mp4 files. Use this online video converter to transcode between MP4 (H.264), WebM (VP9), MKV, MOV, AVI, Animated GIF, and audio-only MP3 / AAC / Opus 100% locally in your browser via FFmpeg WebAssembly.

When container formats and codecs block your workflow

A video file has two layers: the outer container (.mp4, .mov, .mkv, .webm, .avi) and the inner video/audio codecs (H.264, HEVC, VP9, AAC, Opus). Most upload errors happen when a website or editing program accepts the codec but rejects the outer container, or vice versa.

For example, OBS Studio recommends recording screen captures to MKV because an MKV file stays readable even if your PC loses power mid-stream. However, Adobe Premiere, Final Cut, and most web portals refuse to import .mkv files until they are converted into an MP4 container. Similarly, sending an Apple QuickTime .mov file to a Windows colleague or embedding it in an HTML5 <video> tag often results in a black screen or missing audio until it is transcoded to H.264 MP4 or VP9 WebM.

This workspace also handles video-to-audio extraction: when you recorded a 30-minute Zoom meeting, lecture, or concert video and only need the audio track as an MP3, AAC, or Opus file for your phone or transcription tool, selecting an Audio-Only output format discards the video stream and exports the sound track in seconds.

How to use the online video converter in four steps

  1. Drag your video file (MP4, MOV, MKV, WebM, AVI, FLV, or WMV) into the upload area or click to browse from your device.
  2. Select your Target Output Format: choose a video container (MP4 H.264, WebM VP9, MKV, MOV, AVI, Animated GIF) or an audio-only format (MP3, AAC, Opus).
  3. Pick your Resolution (Same as Source, 1080p, 720p, or 480p), Quality Preset (High CRF 20, Medium CRF 26, or Low CRF 32), frame rate (FPS), or set optional Trim Start / End timestamps.
  4. Click Convert Video, monitor the live WebAssembly encoding progress, preview the finished file in the built-in player, and click Download.

Video transcoding, audio extraction, and resolution controls

Powered by a client-side FFmpeg WebAssembly pipeline, the converter gives you control over both video and audio streams without touching a command line.

  • Six video containers + three audio-only extractors: Convert across MP4, WebM, MKV, MOV, AVI, and GIF, or rip the audio stream directly to MP3, AAC, or Opus.
  • CRF quality & resolution scaling: Keep the original frame dimensions or downscale to 1080p, 720p, or 480p while choosing between High (CRF 20) for archival clarity, Medium (CRF 26) for everyday sharing, or Low (CRF 32) for compact files.
  • Frame rate & audio track options: Lock output frame rate to 60 fps, 30 fps, or 24 fps, or strip the audio track completely when creating silent web loops.
  • Built-in sub-clip trimmer: Enter exact start and end timestamps before converting so you only transcode the highlight clip you actually need.
  • Live terminal & progress telemetry: Shows exact encoding percentage and output byte size right in the browser.

Worked example: converting an OBS .MKV recording to MP4 and MP3

Suppose you record a 3-minute, 20-second software tutorial in OBS Studio saved as Tutorial-Capture.mkv (1920 x 1080 at 60 fps, 68.5 MB). You need two deliverables:

  1. A universal 1080p MP4 file to upload to your learning portal.
  2. An MP3 audio file of the voiceover to run through a subtitle generator.

Inside the converter:

  • Pass 1 (Video to MP4): You load Tutorial-Capture.mkv, select MP4 (H.264), keep Resolution = Same as Source (1080p), and choose Quality = High (CRF 20). The converter outputs Tutorial-Capture.mp4 (41.2 MB), which plays natively in every browser and imports into any video editor.
  • Pass 2 (Video to MP3 Audio): Without re-uploading, you switch the Target Format dropdown to MP3 (Audio Only) and click Convert. Because the video frames are skipped completely, the encoder extracts the 200-second voiceover track in under 3 seconds, producing Tutorial-Capture.mp3 at 3.1 MB.

Practical tips for fast in-browser video conversion

Keep these three tips in mind to get the fastest conversion speeds in a web browser:

  1. Audio extraction is near-instant: Converting a 500 MB MP4 or MKV video into an MP3, AAC, or Opus audio file skips video frame encoding entirely, so even a 20-minute video converts to audio in a few seconds.
  2. Match resolution to your screen target: If your source file is a 4K (3840 x 2160) phone video that will only be watched in a 720p web player or chat window, selecting 720p in the Resolution dropdown cuts encoding time by roughly 75% and prevents browser tab memory spikes.
  3. Keep animated GIF exports focused on short clips: If you choose GIF (Animated) as your target format, use the Trim Start / End boxes to isolate a 3-to-8-second moment and select 480p, or open our dedicated Animated GIF Maker for frame-by-frame captioning and ping-pong loop controls.

Local WebAssembly execution and privacy

Your source video and converted output files remain 100% inside your browser's local memory sandbox. No video streams or audio tracks are ever uploaded to a remote server.

Choosing between MP4 (H.264), WebM (VP9), and audio-only MP3 extraction

Each container format in the converter serves a specific playback ecosystem:

  • MP4 (H.264 + AAC): The universal standard. Plays natively with hardware acceleration on every Windows PC, Mac, iPhone, iPad, Android phone, Smart TV, and social media upload form. Whenever an iPhone .mov (HEVC) or screen-recorded .mkv / .webm won't open in an editor or client laptop, converting to MP4 solves it.
  • WebM (VP9 + Opus): Royalty-free open web video format favored for HTML5 <video> background loops and modern browser embeds at compact file sizes.
  • Extract Audio to MP3: Strips the video track completely and encodes only the stereo/mono audio stream, which is ideal for turning a recorded 45-minute Zoom/Meet .mp4 lecture or webinar into a compact .mp3 you can listen to on the go.

Related video, audio, and subtitle tools

If your primary goal is shrinking an MP4 under a strict megabyte cap, use the Video Compressor & Trimmer. For normalizing volume or converting standalone audio files, open the Audio Converter. You can also build captioned loops in the Animated GIF Maker, fix out-of-sync captions using the Subtitle Time Shifter, or see our guide on how to convert video to MP4 in your browser.

Frequently Asked Questions

Why can I not play or import .MKV or .MOV files on certain devices until I convert them to .MP4?

MKV (Matroska) and Apple QuickTime MOV are container formats that many web browsers, Windows apps, and smart TVs do not support natively. Converting them to an MP4 container with H.264 video and AAC audio ensures universal playback across every operating system. Powered by FFmpeg compiled to WebAssembly, this converter transcodes video files between MP4 (H.264/AAC), WebM (VP9/Opus), MKV, MOV, AVI, and Animated GIF in your browser.

How do I extract just the MP3 audio from an MP4 or MKV video file?

Upload your video file and open the Target Format dropdown. Scroll to the Audio-Only section and select MP3 (Audio only), AAC, or Opus. The converter will discard the video stream and export only the audio track in seconds. Selecting an Audio-Only target format (MP3, AAC / M4A, WAV, or OGG Opus) strips the video track and extracts a clean audio file from lectures, interviews, or music clips.

What do CRF 20, CRF 26, and CRF 32 mean in the Quality dropdown?

CRF stands for Constant Rate Factor, the quality scale used by H.264 and VP9 encoders. Lower numbers mean higher quality and larger files: CRF 20 is near-lossless visual quality, CRF 26 is the balanced everyday standard, and CRF 32 prioritizes small file size. You can combine format conversion with Resolution Scaling (1080p, 720p, 480p), Frame Rate (FPS) adjustment, and Start / End Time Trimming in a single pass.

Are my videos uploaded to the cloud during conversion?

The converter runs FFmpeg compiled to WebAssembly directly inside your browser tab, using your computer’s own CPU and RAM. Your video files never leave your device. Converting Apple QuickTime .mov or .mkv screen recordings into standard .mp4 (H.264) guarantees universal playback across Windows, Android, Slack, Discord, and web browsers.

Can I trim a long video so only a 15-second clip gets converted?

Enter the start second and end second in the Trim Start and Trim End boxes before clicking Convert. Only the frames inside that time window will be transcoded and saved. For reliable in-browser WebAssembly memory allocation on desktop computers, keep individual source videos under roughly 500 MB to 1 GB (150–200 MB on mobile).

What is the maximum video file size I can convert in a browser?

On desktop browsers (Chrome, Edge, Brave, Firefox) with 8 GB+ of system RAM, files up to 500 MB–1 GB convert reliably. On mobile devices, keeping clips under 150–200 MB prevents browser tab memory reloads. Your video files are read and transcoded 100% locally on your own hardware without ever uploading private recordings to a remote server.