50 KB M4A sample

An M4A file of exactly 51,200 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 50 KB sample, test or dummy M4A file.

sample-m4a-50kb.m4a

50 KB51,200 bytes

Download 50 KB M4A

Created in your browser in a few seconds, then checked against the SHA-256 checksum. The file is not uploaded anywhere. No sign-up.

Type: audio/mp4
SHA-256: b64d03d07ad3c63cb80585fcbdf08b0494659f197846711574ceb1ae0b3e3f71
Delivery: Created in your browser from static generator assets (how it works).

What is in this file

136 AAC frames (3.2 s) of a synthesised musical phrase that repeats every eight seconds, in one audio track. 174 bytes of a trailing "free" box bring the file to the exact size.

Duration	3.2 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-50kb.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 00 04 60 |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 00 0c 56 |.{i..{i........V|

Preview

Creates the file in your browser and shows it here.

Where 50 KB matters

A 51,200-byte file, half of the default body limit in several web frameworks. These are the default limits a file of this size is useful for testing:

System	Limit	Note
Express body parsers	100 KB by default	50 KB is accepted; 500 KB is rejected with 413 unless the limit is raised.
Base64 encoding	Adds 33 percent	50 KB becomes about 67 KB when embedded in JSON.

All 50 KB sample files

Use this file for

Checking email size handling
Checking podcast and audiobook pipelines
Verifying type detection between audio and video MP4

Testing notes for M4A

Three media types are in circulation: audio/mp4, audio/x-m4a and audio/m4a. Browsers send different ones for the same file.
The container is the same as MP4 video, so content sniffers often report video/mp4. Telling them apart takes a look at the ftyp brand or at the tracks.

M4A format reference

Technical details

File name	sample-m4a-50kb.m4a
Format	M4A (MPEG-4 audio)
Extension	.m4a
MIME type	audio/mp4
Size	51,200 bytes (50 KB)
Kind	Binary
Signature	66 74 79 70 4D 34 41 20 at offset 4
SHA-256	b64d03d07ad3c63cb80585fcbdf08b0494659f197846711574ceb1ae0b3e3f71
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-50kb.m4a     # Linux
shasum -a 256 sample-m4a-50kb.m4a # macOS

On Windows, run Get-FileHash sample-m4a-50kb.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 50 KB?: Yes. It is 51,200 bytes, which is 50 KB in the binary units that operating systems and server limits use (1 KB = 1,024 bytes).
What is inside the 50 KB M4A file?: 136 AAC frames (3.2 s) of a synthesised musical phrase that repeats every eight seconds, in one audio track. 174 bytes of a trailing "free" box bring the file to the exact size.
Is an M4A file the same as an AAC file?: Not quite. M4A is AAC inside an MP4 container, with an index that allows seeking. A file ending in .aac is a bare stream of AAC frames with a small header on each and no index.

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