MP4 Converter Online – H.264/AAC or Stream Copy

Convert MKV, AVI, MOV, WebM and other videos to MP4. Re-encode to H.264/AAC or stream-copy compatible codecs in your browser.

Click for theater mode

Drop video files here

Add a supported video. Conversion uses browser CPU and RAM; large files may fail on limited devices.

Conversion Mode

Add videos to convert to MP4.

Selected videos are processed in your browser and are not uploaded by the converter.

Conversion Queue

0 videos total

Your videos will appear here.

How to Use

  1. Drag and drop your video files into the upload area or click "Select Files". You can add multiple videos for batch processing.
  2. Keep Re-encode to H.264/AAC selected for a new H.264/AAC output. Choose Stream Copy only when the source streams already fit MP4.
  3. Click "Convert to MP4". The browser downloads FFmpeg on first use and processes queued files one at a time.
  4. Download each MP4 and test it in the target player. A container or codec change cannot cover every device constraint.

Core Features

  • H.264/AAC Re-encode by Default: Decode the input and create H.264 video at CRF 23 with AAC audio at 128 kbps in an MP4 container.
  • Optional Stream Copy: Repackage compatible source streams without re-encoding. This avoids a new encoding pass but cannot fix an unsupported codec.
  • Common Video Inputs and Batch Queue: Add multiple MOV, MKV, AVI, WebM, FLV, WMV, M4V, 3GP, or TS files when the browser FFmpeg build can decode them.
  • Browser Processing with Device Limits: Selected inputs are not uploaded by the converter. FFmpeg loads on first use, and large videos can exhaust CPU or RAM.

For MOV-only container conversion, use the MOV to MP4 converter. For a device-oriented check, see MP4 for PSP or video to Android MP4.

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Calculation Logic

MP4 is a container; actual playback depends on the codecs, profiles, resolution, and target player. The default mode uses FFmpeg WebAssembly to encode H.264 with the ultrafast preset at CRF 23 and AAC at 128 kbps. Re-encoding is lossy.

Stream copy runs without a new encode and therefore adds no new encoding loss, but it succeeds only when the source streams are valid inside MP4. Both modes use browser memory for the input, engine, and output.

FAQ

Is there a practical file-size limit?

The UI does not impose an upload cap, but browser memory and device CPU create a real limit. Very large or long videos can slow down, fail, or crash the tab.

What is the difference between "Deep Re-encode" and "Fast Stream Copy"?

  • Stream Copy repackages compatible streams without a new encode. It does not change the codecs.
  • Re-encode creates H.264 video at CRF 23 and AAC audio at 128 kbps. It is slower, uses more resources, and is lossy.

Are selected videos uploaded?

The converter reads selected files into the browser FFmpeg file system and does not upload them to a conversion service. A network connection is still required to load the engine when first needed.

Why do huge videos take a long time and sometimes crash the browser?

Re-encoding recalculates frames and keeps several large buffers in browser memory. If RAM is limited, close other tabs, shorten the video, or use native desktop software.