Video Format Converter for WebM to MP4
Convert WebM and other supported video inputs to MP4 locally with quick presets, quality, resolution, and audio controls. The FFmpeg engine is hosted with the site, loads only when you start processing, and this browser-side version is best for short clips under 200 MiB.
Drop video here or click to upload
MP4 and WEBM are the safest first-version inputs.
Max file size: 200MiB
No video uploaded
Mobile processing guidance
On mobile, start with a short MP4/WebM under 50MiB before trying larger clips.
Max 200MiB in this browser version.
FFmpeg uses this tab's CPU and memory after you start processing.
If processing stalls, stop and retry with a shorter clip, lower resolution, or higher CRF.
File limit
Use files under 200MiB. Smaller clips are more reliable on mobile.
Processing time
FFmpeg loads after you click the action button, then uses local CPU and memory.
Common failures
Unsupported codecs, low memory, very large files, or long clips can fail.
Quick conversion presets
Start from the target player or upload surface, then adjust quality, resolution, or audio.
Output MP4
H.264 video with AAC audio for broad compatibility. WebM/VP9 video encoding is unavailable because the bundled encoder is unreliable. WebM input is still supported when decodable.
Keep the source dimensions.
Disable for a smaller silent video.
Engine
ffmpeg.wasm
Output
MP4
Audio
128 kbps
Frame rate
Source FPS
Next step
Choose a short MP4 or WebM first. On mobile, start under 50MiB before trying larger clips.
Output size
No converted video yet
Format
MP4
Size change
Not ready
Processing
Not ready
FFmpeg is designed to run in the browser only after you start processing, and the large WebAssembly engine is served from this site.
A video format converter re-encodes a source video into a different browser-friendly output format.
This version exports MP4. WebM/VP9 video encoding is temporarily unavailable; WebM inputs can still be converted to MP4.
Choose MP4 compatibility or Mobile upload MP4 before adjusting quality, resolution and audio manually.
FFmpeg loads only when you start processing; large files, unsupported codecs, and mobile browsers can still run into memory limits, so use desktop for larger clips.
Short clips under 200 MiB
MP4, WEBM, MOV, and other common containers are the best first inputs for this browser-side conversion flow.
Destination format choice
Use MP4 compatibility or Mobile upload MP4, then check the destination player or upload form.
Mobile and slower devices
Use shorter clips or lower resolution on mobile because ffmpeg.wasm conversion can be memory intensive.
Desktop for large clips
If the source is long, high resolution, or near 200 MiB, use a desktop browser or desktop video software before retrying.
WebM to MP4 upload
Convert a browser recording to a format accepted by more upload forms.
Input
A WebM screen recording exported from a browser tool.
Settings
- Preset: MP4 compatibility
- Keep audio
- Original resolution
Expected output
An MP4 file with broader upload compatibility.
Mobile MP4 upload
Create an MP4 version at a smaller resolution for an upload form.
Input
A short MP4 product clip.
Settings
- Preset: Mobile upload MP4
- Quality: balanced
- Limit resolution to 720p
Expected output
An MP4 output to test in the destination upload flow.
Silent MP4 preview
Make a silent loop-style clip when GIF would be too heavy.
Input
A short MP4 animation snippet.
Settings
- Preset: MP4 compatibility
- Remove audio
- Max height: 480px
Expected output
A silent MP4 preview; check its actual file size before replacing an existing asset.
Know the upload target
Confirm that the destination accepts H.264/AAC MP4 before changing quality settings.
Check size and duration
Files over 200 MiB are rejected in this version, and long high-resolution clips are better handled on desktop.
Expect re-encoding
Conversion creates a new file; it can change codec, audio behavior, metadata, and file size.
Use desktop for heavy files
Mobile browsers are best for short tests. Move long, 4K, or near-limit files to a desktop workflow.
Choosing a format without a target
Pick the destination first: upload form, chat app, browser page, mobile preview, or documentation embed.
Expecting every codec to decode
FFmpeg supports many formats, but browser memory and WebAssembly limits still matter. Common MP4 and WebM inputs are safest.
Treating all failures the same
Codec unsupported, memory limit, file too large, and long high-resolution clips need different retries.
Confusing conversion with compression
Changing container format does not guarantee a smaller file. Use the video compressor when file size is the main goal.
Ignoring destination support
Use the MP4 output and test it in the final platform before publishing.
Compatibility
Convert WebM or MOV clips to MP4 before uploading to systems that expect MP4.
Mobile uploads
Use an MP4 output preset with a practical resolution when a phone-first platform rejects the original file.
Preview exports
Create a smaller preview version while keeping the original source file private.
Local testing
Test downloaded MP4 playback, dimensions and audio before sharing.
Input/output matrix
WebM and other supported sources can become MP4; WebM/VP9 output is currently unavailable.
Processing stages
The tool loads FFmpeg, writes the source file, converts locally, reads the output, then creates a downloadable file.
Failure explanations
Unsupported codecs, low memory, files near 200 MiB, and long high-resolution clips are separate failure modes.
Use desktop for large files
Desktop browsers and desktop video tools are more reliable for long, 4K, or near-limit conversion jobs.
Audio choice matters
Removing audio can make preview clips simpler, but keep audio when the destination needs narration or sound.
Compression is separate
Use the compressor when the primary goal is a smaller file, not just a different format.
How is the video converted?
The selected video is designed to be processed in your browser with ffmpeg.wasm based on the current public implementation. Avoid sensitive files unless you have reviewed the implementation.
Which output formats are supported?
MP4 with H.264 video and optional AAC audio is available. WebM/VP9 video encoding is temporarily unavailable because the current encoder fails on validated inputs. WebM input remains supported.
What preset should I start with?
Use MP4 compatibility for broad uploads or Mobile upload MP4 for a smaller resolution. Turn off audio manually when a silent MP4 is needed.
Can it convert every video format?
No. FFmpeg can read many containers, but browser memory, codec support, and WebAssembly limits still matter. Use smaller files and common inputs for the best result.
Why did conversion fail?
Common causes are an unsupported source codec, not enough browser memory, a file near the 200 MiB limit, or a long high-resolution clip. Retry with a shorter file, original resolution, MP4/WebM input, or a desktop browser.
Is conversion the same as compression?
No. Conversion changes the output format or codec. Compression focuses on reducing size with quality, resolution, and bitrate choices.
Suggested workflow
Build a browser-side video conversion workflow
Choose the converter for a format change, or the compressor when a size target is the main goal. Avoid exporting through both unless the first result is insufficient.
Guides and examples