20 MB MP4 sample file

An MP4 file of exactly 20,971,520 bytes. It is a valid MPEG-4 Part 14 video file, generated for this site and checked with an independent parser. Use it wherever you need a 20 MB sample, test or dummy MP4 file.

sample-mp4-20mb.mp4

20 MB20,971,520 bytes

Download 20 MB MP4

Created in your browser in a few seconds, then checked against the SHA-256 checksum. No sign-up.

Type: video/mp4
SHA-256: c9b2cd1f5f2b1fed94a2da1f96c39c7f5a2951acc8ab6c11f47e014f4645249e
Delivery: Created in your browser. Files of 2 MB and more have no direct URL (why).

What is in this file

11,186 frames (6 min 13 s) of a synthetic test pattern with a frame counter, looping every six seconds, in one H.264 video track. 505 bytes of a trailing "free" box bring the file to the exact size.

Dimensions	640 × 360 px
Duration	6 min 13 s
Frame rate	30 fps
Video codec	H.264 (AVC), Main profile
Audio	No audio track
Fast start	Yes (moov before mdat)

First bytes of the file

The first 64 bytes of sample-mp4-20mb.mp4 as a hex dump: offset, bytes, then the same bytes as text. The MP4 signature is 66 74 79 70 at offset 4.

00000000  00 00 00 20 66 74 79 70 69 73 6f 6d 00 00 02 00  |... ftypisom....|
00000010  69 73 6f 6d 69 73 6f 32 61 76 63 31 6d 70 34 31  |isomiso2avc1mp41|
00000020  00 00 bc ef 6d 6f 6f 76 00 00 00 6c 6d 76 68 64  |....moov...lmvhd|
00000030  00 00 00 00 e5 7b 69 80 e5 7b 69 80 00 00 03 e8  |.....{i..{i.....|

Preview

Creates the file in your browser and shows it here. Nothing large is downloaded from our server.

Where 20 MB matters

A 20,971,520-byte file: right at the default attachment limit of Outlook, and just under the 25 MB ceilings of Gmail and GitHub web uploads. These are the default limits a file of this size is useful for testing:

System	Limit	Note
Microsoft Outlook	20 MB of attachments by default for internet mail accounts	This file is right at the limit; add a second attachment and it is exceeded.
Gmail	25 MB per message	Under the limit, although email encoding adds about a third in transit.
GitHub web uploads	25 MiB per file added through the browser	Accepted. Pushing with Git allows larger files.
Cloudflare Pages assets	25 MiB per file	The largest round size that can be served as a static asset.
Amazon API Gateway	10 MB payload	Rejected; the upload has to go directly to object storage.
ASP.NET Core (Kestrel)	About 28.6 MB request body by default	Accepted with room for the multipart overhead.

All 20 MB sample files

Use this file for

Testing email attachment limits
Testing video upload, transcoding and thumbnail extraction
Checking HTML video playback and seeking

Testing notes for MP4

Seeking in a browser needs HTTP range requests. A server that ignores the Range header makes video appear to work until someone drags the progress bar.
A valid .mp4 may contain a codec the browser cannot play; container and codec are separate questions.

MP4 format reference

Technical details

File name	sample-mp4-20mb.mp4
Format	MP4 (MPEG-4 Part 14 video)
Extension	.mp4
MIME type	video/mp4
Size	20,971,520 bytes (20 MB)
Kind	Binary
Signature	66 74 79 70 at offset 4
SHA-256	c9b2cd1f5f2b1fed94a2da1f96c39c7f5a2951acc8ab6c11f47e014f4645249e
Created	2026-10-14
Validation	Exact size, signature bytes and structure checked when the generator was built; your copy is checked against the SHA-256 after it is created
Preview	Available on this page
Source	Generated in your browser by this site's generator; not copied from elsewhere
Licence	Free to use, modify and redistribute (terms)
Category	Video

Validated for expected format and integrity. As with any download, scan the file with your own security tools before opening it. How files are made and checked

Verify your copy

This file is created in your browser, so it has no direct URL for curl or wget. The bytes are the same every time and in every browser, so after saving it you can compare its checksum with the SHA-256 value above.

sha256sum sample-mp4-20mb.mp4     # Linux
shasum -a 256 sample-mp4-20mb.mp4 # macOS

On Windows, run Get-FileHash sample-mp4-20mb.mp4 -Algorithm SHA256 in PowerShell. For scripts and pipelines, save the file once and keep your own copy, or use a 1 MB file, which has a direct URL.

Related files

Questions about this file

Is this file exactly 20 MB?: Yes. It is 20,971,520 bytes, which is 20 MB in the binary units that operating systems and server limits use (1 KB = 1,024 bytes).
What is inside the 20 MB MP4 file?: 11,187 frames (6 min 13 s) of a synthetic test pattern with a frame counter, looping every six seconds, in one H.264 video track. 356 bytes of a trailing "free" box bring the file to the exact size.
Do the MP4 samples have sound?: No. They contain a single H.264 video track and no audio track.

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