When you submit a class assignment, application, or contest video online, reducing file size is only part of the job. The result must also match the portal's format, duration, resolution, aspect-ratio, and naming rules. This guide uses 100MB as an example; the receiving site's instructions always take priority.
Rather than aiming for exactly 100MB, a practical target of about 90–95MB leaves room for different size calculations and small encoding variations caused by motion and scene complexity.
Start with these choices
Check maximum size, MP4 support, duration, resolution, aspect ratio, and file-name rules before encoding.
For a 100MB limit, 90–95MB is a practical target that reduces borderline upload failures.
Verify the beginning, ending, audio, captions, aspect ratio, and actual size in the final output.
Use this order to reduce repeat attempts
Set the submission requirements and target before opening a compressor, then treat playback review as part of the workflow.
- Copy the portal's maximum size, accepted format, duration, resolution, aspect-ratio, and file-name requirements into a checklist.
- Keep the original and set the submission copy's target 5–10% below the stated limit.
- Start with MP4 and a resolution close to the source; if the result is too large, step down from 1080p to 720p before crushing quality.
- Play the downloaded file from start to finish, then verify audio, captions, file size, extension, and name before uploading.
Check more than the file-size limit
Compressing immediately after seeing ‘100MB maximum’ can still leave you with the wrong format, an overlong video, or an unsupported aspect ratio. Read the full submission specification first.
When a portal asks for MP4 but does not name codecs, H.264 video with AAC audio is a broadly compatible choice across browsers and PCs. A specification supplied by the recipient overrides this general recommendation.
- Maximum file size
- Accepted container and codecs
- Maximum duration
- Resolution and aspect ratio
- File-name and deadline rules
For a 100MB limit, aim around 90–95MB
A file browser and an upload portal may display sizes differently. Some use 100,000,000 bytes for 100MB, while operating systems may present binary-based values under familiar labels. A result sitting on the boundary can pass locally and fail on the portal.
The 90–95MB range is an operational safety margin, not a universal submission rule. Follow any exact calculation method published by the recipient.
Longer videos have fewer bits available per second
If two videos must fit the same 100MB limit, the longer one has less data available for every second. A one-minute clip and a ten-minute presentation cannot retain the same visual quality at the same final size.
A mostly static presentation usually compresses more efficiently than sports, games, foliage, water, grain, or rapid camera movement. Complex motion can look blocky sooner at the same target size.
720p can look better than an over-compressed 1080p result
Keeping every 1080p pixel under a strict size limit can leave too little information per pixel. Reducing the frame to 720p may produce a cleaner result because the available data is spread across fewer pixels.
For screen recordings, diagrams, or lectures with small text, test a representative section before reducing resolution. The resolution number alone does not tell you whether the content remains readable.
A target size is an estimate, not a promise
Video encoders can allocate data differently from scene to scene. Motion, noise, cuts, and texture make two files with the same length and resolution finish at different sizes.
If the first result is slightly too large, lower the target or resolution one step instead of immediately selecting the lowest quality. If it is far below the limit and important details look soft, you may have room to raise the target or resolution.
Inspect the output, not only the source
A working source does not guarantee a working submission copy. Open the downloaded MP4 separately and check that the beginning and ending are present, audio is synchronized, captions are readable, and orientation is correct.
Finally confirm the actual file size, extension, duration, and required file name. Keep the source and submission copy clearly separated to avoid uploading the wrong version.
- Play the beginning, middle, and end
- Check audio and synchronization
- Read the smallest caption or slide text
- Confirm orientation and aspect ratio
- Verify size, extension, duration, and file name
Frequently asked questions
Should I make the file exactly 100MB for a 100MB limit?
No. Aim around 90–95MB unless the recipient provides a different calculation rule. The margin helps with size-display differences and encoding variation.
Are 100MB and 100MiB the same?
No. MB commonly uses powers of 1000, while MiB uses powers of 1024. Interfaces sometimes use the labels loosely, which is another reason to leave a margin.
Should I keep 1080p or reduce the video to 720p?
It depends on duration and content. A heavily compressed 1080p file can look worse than a cleaner 720p result, while small text may still require more resolution. Test a representative section.
Why do two videos finish at different sizes with the same settings?
Motion, noise, texture, and scene changes affect how much data the encoder needs. Treat the target as an estimate and inspect the final size.
Can MOV or WEBM be converted to a submission-ready MP4?
Supported inputs can be encoded as MP4. Still verify any codec, resolution, duration, and naming requirements published by the submission portal.