20 MB WebM sample

A WebM file of exactly 20,971,520 bytes. It is a valid WebM video file, generated by this site. Compare its checksum and test it with the parser used by your application. Use it wherever you need a 20 MB sample, test or dummy WebM file.

sample-webm-20mb.webm

20 MB20,971,520 bytes

Download 20 MB WebM

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

Type: video/webm
SHA-256: 7549fcc617cd88b6e52b441da9261038cdd352cf5a7817d143b7c53b684654b3
Delivery: Created in your browser from static generator assets (how it works).

What is in this file

16,305 frames (9 min 4 s) of a synthetic test pattern with a frame counter, looping every six seconds, in one VP9 video track. The index of key frames comes before the picture data, so a player can seek without reading the whole file. 746 bytes of an EBML Void element bring the file to the exact size.

Dimensions	640 × 360 px
Duration	9 min 4 s
Frame rate	30 fps
Video codec	VP9
Audio	No audio track
Document type	webm
Clusters	544, one for each key frame
Seek index	Cues element before the first cluster

First bytes of the file

The first 64 bytes of sample-webm-20mb.webm as a hex dump: offset, bytes, then the same bytes as text. The WebM signature is 1A 45 DF A3.

00000000  1a 45 df a3 9f 42 86 81  01 42 f7 81 01 42 f2 81 |.E...B...B...B..|
00000010  04 42 f3 81 08 42 82 84  77 65 62 6d 42 87 81 04 |.B...B..webmB...|
00000020  42 85 81 02 18 53 80 67  01 00 00 00 01 3f ff d0 |B....S.g.....?..|
00000030  11 4d 9b 74 b3 4d bb 8e  53 ab 84 15 49 a9 66 53 |.M.t.M..S...I.fS|

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 image resizing and memory use
Verifying type detection between WebM and MKV
Testing transcoding from WebM to MP4

Testing notes for WebM

WebM and MKV share a signature, so a sniffer has to read the document type to tell them apart.
H.264 and AAC are not allowed in WebM. A file with those codecs and a .webm extension is really Matroska, and browsers may refuse it.

WebM format reference

Technical details

File name	sample-webm-20mb.webm
Format	WebM (WebM video)
Extension	.webm
MIME type	video/webm
Size	20,971,520 bytes (20 MB)
Kind	Binary
Signature	1A 45 DF A3
SHA-256	7549fcc617cd88b6e52b441da9261038cdd352cf5a7817d143b7c53b684654b3
Created	2026-10-23
Validation	See the listed size and SHA-256. Small downloads are checked in the browser; verify streamed downloads manually. A hash match does not prove parser compatibility.
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

Check the stated structure and checksum against your application requirements. 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 generator is designed to produce reproducible bytes. After saving, compare the checksum with the SHA-256 value above.

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

On Windows, run Get-FileHash sample-webm-20mb.webm -Algorithm SHA256 in PowerShell. For scripts and pipelines, save the file once and keep your own copy.

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 WebM file?: 16,305 frames (9 min 4 s) of a synthetic test pattern with a frame counter, looping every six seconds, in one VP9 video track. The index of key frames comes before the picture data, so a player can seek without reading the whole file. 746 bytes of an EBML Void element bring the file to the exact size.
Which codec do the WebM samples use?: VP9 video at 640 × 360 and 30 frames per second, with no audio track.

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