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Audio & video / Local FFmpeg tool

Video to MP4 Converter

Transcode video to H.264/AAC MP4 with adjustable quality and browser-friendly pixel format.

● Files stay in your browser
Files stay in your browser

The first run loads an approximately 31 MB FFmpeg WebAssembly core from this site. It does not use a CDN or upload your files.

Files are limited to 200 MB total and 20 minutes; mobile devices use an 80 MB limit. Reverse, GIF and boomerang tools have lower duration caps.

Choose files, set the controls, then start.Progress: 0%

Processed result

The first run loads an approximately 31 MB FFmpeg WebAssembly core from this site. It does not use a CDN or upload your files.

Validated downloads will appear here after processing.

Method, example & boundaries

Video to MP4 Converter: from input to a reviewable result

Transcode a common local video container to an H.264 video and AAC audio MP4 with explicit quality control. This is a compatibility conversion rather than a filename change: streams are decoded, re-encoded, and validated in the resulting container.

Worked example: convert a camera MOV for browser playback

Example input
1920×1080 MOV, 45 seconds; CRF 23.
Example output
One 1920×1080 MP4 using H.264, AAC, and yuv420p, with output duration checked.

How to interpret it

The original container alone does not guarantee browser compatibility. Re-encoding the streams and pixel format creates a more predictable delivery file.

Browser-local compatibility transcode

FFmpeg.wasm probes source streams, decodes them, encodes H.264 video at the selected CRF and AAC audio, writes yuv420p MP4, then probes width, height, duration, and format before reporting success.

MP4 conversion boundaries

  • Re-encoding takes time and can increase size when the source was already efficiently compressed.
  • Alpha channels, HDR metadata, subtitles, chapters, and secondary streams are not guaranteed to survive.
  • The browser workflow is capped by device memory, file size, and a 20-minute duration limit.

Local AI / Speech to text

Transcribe the current audio or video

Open-source Whisper Tiny runs in your browser. The file, audio and result are never uploaded.

◎ First use loads about 64 MB of model and runtime files

Choose an audio or video file in the workbench above first.

◎ The model loads only from 321Kit; MiniMax is not called and no transcript history is stored.

Transformers.js + Whisper Tiny (Apache-2.0)

Transcript

How it works

Video to MP4 Converter

CRF controls H.264 quality: lower values retain more detail and produce larger output.

How does this tool process my file?

CRF controls H.264 quality: lower values retain more detail and produce larger output. Processing uses single-thread FFmpeg.wasm. The page does not upload, store or inspect file content outside this device. Cancel, error and page close terminate the worker and revoke temporary object URLs.

What limits apply to the output?

Output uses H.264, AAC and yuv420p; alpha channels are not preserved. Files are limited to 200 MB total and 20 minutes; mobile devices use an 80 MB limit. Reverse, GIF and boomerang tools have lower duration caps.

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