How to Compress a Video Online for Free: Reduce MP4 File Size

If you're not tech-savvy, use the free online video compressor tool to shrink your video file size. Just pick your video, set a target size in megabytes or adjust quality controls, choose MP4 as the output, enable resizing if needed, and then convert and download the compressed video. No installation or account creation is required.

If you're more technically inclined, you can re-encode the video locally using FFmpeg for a more customized approach. Open the FFmpeg command with your input video, select the video and audio streams, and encode them using H.264 video compression and AAC audio compression. Control the quality with the CRF setting, which doesn't specify a fixed size. After encoding, compare the output to the original file to ensure the desired reduction in size.

When reducing a video's file size, duration plays an important role alongside resolution. As a general rule, file size is roughly proportional to duration multiplied by combined video and audio bitrate divided by eight. For example, a 60-second video with a total bitrate of 2 megabits per second would need around 15 megabytes before container overhead. So, for longer recordings, a lower bitrate may be necessary to fit the same size limit.

Remember that MP4 is just a container format, not a size setting. Two MP4 files with the same duration can have different sizes due to differences in encoded bitrates, resolutions, frame rates, and audio settings. Always choose the appropriate output format and use compression controls to manage file size effectively.

Keep in mind that while MP4 is a convenient format for web use, reducing video size also means losing some quality. If you need to preserve important details, like text or fine details, consider lowering the compression level or resolution carefully. Always keep the original video file as a backup, since once you apply lossy compression, you can't recover the lost quality.