Media · MP4
A 20 MB MP4 file, on demand.
Exactly 20,971,520 bytes of an ISO Base Media container with correct ftyp branding, built on your machine the moment you press the button.
20,971,520 bytes, exactly.
Every byte above the 48 bytes structural minimum goes into a free box, the container’s own reserved-space atom, which is why this file still behaves like one a real user would send.
Unit convention
20 MB on this page means exactly 20,971,520 bytes, using the binary (MiB) convention some systems label "MB" for short. 1 MB in the strict decimal sense is 1,000,000 bytes; 1 MiB is 1,048,576 bytes — the readout above always shows the exact count either way.
Approximate size equivalents
Roughly 11,651 pages of typed text, 22 minutes of 128 kbps audio, 2 minutes of CD-quality audio, 8.4 photos from a 12 MP camera. These figures compare file size only — the generated file does not contain this text, audio or image content.
Accepted by
Outlook.com attachment, Gmail attachment, Cloudflare Free proxy body — all publish a limit at or above this size, based on commonly cited figures that can vary by plan and change over time.
Rejected by
Discord free attachment, AWS API Gateway payload, PHP default upload_max_filesize — this exceeds their commonly cited limit, which makes it a useful negative test. Published limits can vary by plan and change over time.
Other MP4 sizes
Mail servers and chat apps draw the line in this band — Gmail attachments stop at 25 MB, and plenty of APIs cap request bodies alongside them.
20 MB in other media formats
Questions.
Is this 20 MB MP4 file valid?
Yes. It is an ISO Base Media container with correct ftyp branding. The extra bytes sit in a free box, the container’s own reserved-space atom, so it opens in container parsers and ffprobe — note it carries no video track, so it will not play.
Does 20 MB mean 20,971,520 bytes?
On this page, yes — 20 MB uses the binary (MiB) convention, so the file is exactly 20,971,520 bytes. 1 MB in the strict decimal sense would be a different, smaller byte count. Upload validators may use either convention, so the exact byte count is always shown to remove any ambiguity.
What is a 20 MB file used for?
Mail servers and chat apps draw the line in this band — Gmail attachments stop at 25 MB, and plenty of APIs cap request bodies alongside them. For MP4 specifically, the usual job is testing upload size limits where playback is not required.
Where is the file downloaded from?
Nowhere. It is assembled in a Web Worker on your own device and handed to the browser as a Blob, so nothing is uploaded, fetched or stored.