Convert Video Between MP4, WebM, MKV, and MOV in Your Browser

Quick answer

Pick MP4 unless the destination specifically asks for something else. WebM for web embeds that want smaller files. MOV for Apple-first workflows. MKV for personal archiving. The tool decodes and re-encodes the video in your browser; nothing is uploaded.

What each platform actually wants

1. 1

   Load the video

   Drag and drop the file, click to browse, or paste a direct URL on the From URL tab. The tool accepts MP4, MOV, WebM, MKV, and M4V up to 2 GB.

2. 2

   Pick the target container

   MP4 for broad compatibility, WebM for smaller web files, MOV for Apple workflows, MKV for local archiving. The codec choices change to match.

3. 3

   Choose a quality preset

   High preserves visual fidelity at larger file sizes. Medium is a sensible default for upload-ready clips. Low produces small files suitable for chat or quick previews.

4. 4

   Optionally adjust resolution

   Downscale large source video to a target resolution (1080p, 720p, 480p) when the destination does not need 4K. Lower resolutions encode faster and produce smaller files.

5. 5

   Convert and preview

   Click Convert. A progress bar reports encoder progress. When it finishes, the converted file appears with an inline preview player.

6. 6

   Download

   Save the file in the new container. The original stays on your device; the conversion never leaves the browser.

Container vs codec

The container is the file wrapper (MP4, WebM, MKV, MOV). The codec is the compression algorithm inside it (H.264, H.265, VP9, AV1). A given container supports specific codecs; the tool only exposes valid combinations.

Quality preset

Low, Medium, High map to encoder bitrate ladders calibrated for typical content. High is closest to lossless, Low is the smallest file. There is no truly lossless option — every conversion is lossy.

Resolution

Downscaling is the single biggest lever for file size. A 4K source downscaled to 1080p shrinks the file by roughly 4x at the same per-pixel quality. Upscaling does not improve quality and is rarely worth doing.

Hardware acceleration

When the browser supports WebCodecs with hardware encoding (mostly Chrome and Edge on modern hardware), encoding runs several times faster than on CPU. Safari and Firefox often fall back to CPU encoding.

Audio track

Audio is converted along with the video, usually to AAC (MP4, MOV) or Opus (WebM). Audio rarely dominates file size; leave it on default unless you have a specific reason to change it.

Re-encoding cost

Every conversion re-encodes the video, even when the output codec matches the source. Repeated conversions stack generation loss. For multiple edits, convert once at the end.

Realistic scenarios

Videos are decoded and re-encoded inside the browser via the WebCodecs API. No upload, no server processing, no account. URL mode fetches public files directly from the host you paste — CORS and Range request rules apply.

• MP4 + H.264 is the answer to most format questions. Pick something else only when the destination explicitly prefers it.
• Downscale aggressively for clips that will be viewed at small sizes — 720p is more than enough for Slack, Discord, and most chat embeds.
• If a codec is missing from the dropdown, your browser cannot encode it. Try Chrome or Edge for broader codec coverage.
• Convert once at the end of an editing workflow. Repeated conversions stack quality loss.
• Test playback on the actual destination before committing to a batch convert. iMessage, Slack, and email clients each have quirks.

Related video tools

• Video Compressor

  Target a specific file size with bitrate-based compression.

• Video Trimmer

  Cut the clip down before converting to save encoding time.

• Video Resizer

  Change resolution explicitly when format conversion alone is not enough.

• Video to Audio

  Extract the audio track when the video itself is not needed.

Frequently asked questions

Is my video uploaded to a server?

No. The video is decoded, re-encoded, and saved entirely in your browser using WebCodecs. The source file never leaves your device.

Why is one of the output formats greyed out or failing?

Encoding depends on browser-supplied codecs and, for large files, on hardware acceleration. Chrome and Edge support the broadest set. Safari is limited for VP9 and AV1.

Can converting improve video quality?

No. Conversion can change container, codec, resolution, and bitrate, but it cannot restore detail that was lost in the original encoding.

What file size limit applies?

Local files are capped at 2 GB. Very large videos can still exhaust browser memory during encoding, especially on devices with limited RAM. Downscale resolution or pick a lower quality preset for safety.

Does the converter preserve subtitles or chapters?

No. Subtitle tracks and chapter markers are dropped during conversion. If you need to keep them, add them after conversion or work in a desktop tool such as MKVToolNix.

Can I batch convert multiple files?

The tool processes one file at a time. For batches, repeat the conversion with the same settings for each file — the choices stay set between runs.

When should I pick H.265 instead of H.264?

H.265 produces roughly half the file size at the same visual quality, but encoding is slower and playback is not universal on older devices. Use H.264 when in doubt, H.265 for archive or modern-only audiences.

Will MP4 from this tool play in QuickTime?

Yes. The MP4 output uses standard H.264 + AAC, which QuickTime, Final Cut Pro, iMovie, and every modern Apple application accept directly.