20 MB M4A sample

An M4A file of exactly 20,971,520 bytes. It is a valid MPEG-4 audio 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 M4A file.

sample-m4a-20mb.m4a

20 MB20,971,520 bytes

Download 20 MB M4A

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

Type: audio/mp4
SHA-256: d08bdfebf807215611e10bea08a4667d505c68b853ef0416d020049cee5848a6
Delivery: Created in your browser from static generator assets (how it works).

What is in this file

56,089 AAC frames (21 min 42 s) of a synthesised musical phrase that repeats every eight seconds, in one audio track. 150 bytes of a trailing "free" box bring the file to the exact size.

Duration	21 min 42 s
Audio codec	AAC-LC
Bit rate	128 kbit/s
Sample rate	44,100 Hz
Channels	Stereo
Container	MPEG-4 (brand "M4A ")
Fast start	Yes (moov before mdat)

First bytes of the file

The first 64 bytes of sample-m4a-20mb.m4a as a hex dump: offset, bytes, then the same bytes as text. The M4A signature is 66 74 79 70 4D 34 41 20 at offset 4.

00000000  00 00 00 1c 66 74 79 70  4d 34 41 20 00 00 02 00 |....ftypM4A ....|
00000010  4d 34 41 20 6d 70 34 32  69 73 6f 6d 00 03 82 f8 |M4A mp42isom....|
00000020  6d 6f 6f 76 00 00 00 6c  6d 76 68 64 00 00 00 00 |moov...lmvhd....|
00000030  e5 7b 69 80 e5 7b 69 80  00 00 03 e8 00 13 df 70 |.{i..{i........p|

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 audio and video MP4
Testing transcoding to MP3 or Opus

Testing notes for M4A

AAC encoders add a short run of priming samples before the real audio. Players that do not account for it report a slightly longer duration and leave a gap between tracks that should join seamlessly.
Three media types are in circulation: audio/mp4, audio/x-m4a and audio/m4a. Browsers send different ones for the same file.

M4A format reference

Technical details

File name	sample-m4a-20mb.m4a
Format	M4A (MPEG-4 audio)
Extension	.m4a
MIME type	audio/mp4
Size	20,971,520 bytes (20 MB)
Kind	Binary
Signature	66 74 79 70 4D 34 41 20 at offset 4
SHA-256	d08bdfebf807215611e10bea08a4667d505c68b853ef0416d020049cee5848a6
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	Audio

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-m4a-20mb.m4a     # Linux
shasum -a 256 sample-m4a-20mb.m4a # macOS

On Windows, run Get-FileHash sample-m4a-20mb.m4a -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 M4A file?: 56,089 AAC frames (21 min 42 s) of a synthesised musical phrase that repeats every eight seconds, in one audio track. 150 bytes of a trailing "free" box bring the file to the exact size.
Which codec do the M4A samples use?: AAC-LC at 128 kbit/s, 44,100 Hz stereo, which is the combination every device and browser plays.

Download