How to Compress an MP4 Video Online
Follow these three simple steps to compress an MP4 video. No software installation required.
Select an MP4 Video
Choose one MP4 file from your device.
Choose Quality and Resolution
Select a video quality level and keep the original resolution or choose a lower output resolution.
Compress and Download
Start compression, compare the original and output file sizes, and download the compressed video.
How Does the MP4 Compressor Work?
MP4 video compression reduces file size by removing redundant information during re-encoding. CompressFly uses the H.264 codec to retain high visual quality while reducing the amount of data stored in the video. The quality setting controls the balance between file size and visual detail, while a lower output resolution can reduce the size further.
CompressFly handles MP4 compression with modern browser technology. No files are sent to a server: everything is processed locally in your browser. Smart video compression makes reducing MP4 file size simple and free, with no signup required.
What "processed in your browser" means
- Your MP4 file is not uploaded to a server.
- Compression runs locally on your device.
- The compressed video is created in your browser and downloaded directly to your device.
MP4 Compression FAQs
How do I compress an MP4 video online?
Use this online MP4 compressor to reduce MP4 video file size in three steps: 1. Select one MP4 video from your device. 2. Choose the output quality and optional resolution. 3. Compress the video and download the result.
How can I compress an MP4 video without losing quality?
Choose the High quality preset to retain as much visual detail as possible. Keep the original resolution when reducing the dimensions is not necessary.
How does the MP4 compressor reduce file size?
The compressor re-encodes the MP4 video with H.264 at a lower effective bitrate. Bitrate is the main factor that determines file size, while lowering the resolution—for example, from 4K to 1080p—can reduce it further. Everything runs locally in your browser.
How much smaller can an MP4 video get?
Some high-bitrate phone videos and screen recordings can become 50–90% smaller, but this is not guaranteed. An MP4 that is already highly compressed may shrink very little or produce a larger result after re-encoding. The result depends on the source bitrate, resolution, motion, and selected settings.
Which MP4 quality setting should I choose?
Medium balances quality, file size, and processing speed. High retains more detail and usually produces a larger file, while Low favors a smaller file with more visible quality loss. Custom lets you choose a CRF value.
Does lowering the resolution reduce MP4 file size?
It usually can. Reducing a high-resolution video to 1080p, 720p, 480p, or 360p gives the encoder fewer pixels to store, but the result also has lower image dimensions.
Is there an MP4 file size limit, and is my video uploaded?
Your MP4 video is processed locally in your browser and is not uploaded to a server, so there is no server upload limit. The practical limit depends on your device's available memory and processing power, as well as the video's length and resolution.