What Is Octet-Stream? - A Complete Overview

By Ryan Gardner
 on August 30, 2021
Last modified on January 7th, 2022

What Is Octet-Stream? - A Complete Overview

By Ryan Gardner
 on August 30, 2021
Last modified on January 7th, 2022

I have lost count of how many times I tried to open a file attachment that seemed to be blank, in a weird format or did not seem compatible with my available programs.

When possible, I would kindly ask the sender to resubmit the file in a different format. Sometimes I would have to troubleshoot and download different software.

After some research,  I can now say I have encountered octet-stream several times over the years. I am sure many digital media pros have as well. Luckily, it is something that users can troubleshoot with a little information included here.

By the end of the article, you will no longer have to ask "What is octet-stream?".

What is octet-stream?

The application/octet-stream is sent with the header file. If you attempt to download a file with a missing extension or an unknown format, your system will recognize it as an octet-stream file. Any type of file or program can appear on an octet-stream.

For example, your header may send the octet-stream if you are trying to download a Mov.file on a PC but don’t have Quicktime - an Apple program.

The attachment that shows up with octet-stream is a binary file. So you will need an application to properly read and open it - you won’t be able to see it in the body of an email .

If you are knowledgeable about extensions, you may be able to quickly identify which program can open the file. You can also change the extension. A picture file may need its .png extension changed to .jpg . Extensions are covered in further detail below.

What are Binary Files?

Binary files contain data in the form of bytes - not text. The headers in the binary files contain instructions on how to read the data. Only a specific computer processor or program can interpret the file and run it properly.

If you are curious, you can open a binary file in your text editor or notepad, but you will not be able to understand it. The content will look like a series of unique characters.

What Are Some Examples of MIME Extensions?

When you encounter an octet-stream file, being able to identify the extension or general file type can speed up your troubleshooting. It will be easier to  understand what program or application you will need. 

Here are some examples:

  • Audio file extensions - .aac, .avi, .mp3, .wav
  • Video file extensions - mp4, .mpeg
  • Image extensions - .jpg, .png, .tiff, .gif
  • Flash extension -.swf
  • Adobe portable document format- .pdf
  • Microsoft Word extension - .doc, docx
  • Microsof Excel - .xml
  • Compressed files often come in a ZIP file -  .zip

See a more extensive list of extensions here.

How Can I Open an Octet-stream File?

Step 1

Download and double-click the file. It may load correctly if you have the right application. If it does not automatically open, your system will suggest applications to open it with.

You will have to download a suggested application if it is not already installed.

Step 2

Chose a suggested program from the list and click on it.

Step 3

Wait for the file to load. If it does not work, try a different application.

Step 4

Double-click the file once you find a working application. For future downloads of files with his extension, check the box to "Use this app" for all similar files.

Final Note About Octet-stream

This article should now give you a good overview of how to handle octet-stream files. There are many types of attachments or files that you may encounter as you conduct online communication. If you see a future where you have to download tons of  files with a .pdf extension, you may as well download Adobe Acrobat Reader today.

While you should certainly be cautious about opening a strange file, reviewing the extensions above should make you comfortable with downloading octet-stream files.

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John Haley
John Haley
1 year ago

No help here or elsewhere in all of google. Change the extension? Mine is .pages and I see no way to change that. Can't type there. How can that be done?

What would I change it to? How would I know what would work?

If I understand anything, files show up with this octet designation, which isn't really a file type at all, when your PC has nothing that will open the actual file type, which is not revealed for some mysterious reason. So what good is it to try program after program, as I have? The octet designation tells me I can't, have nothing.

Chris B
Chris B
8 months ago
Reply to  John Haley

.pages is from a Mac word processor I believe. Ran into issues trying to view one on Android. Maybe Google Docs or the Onedrive equivalent.

Article By
Ryan Gardner
Ryan is a developer at Isotropic Design, and publishes detailed thoughts, analysis, and comparisons on the Isotropic Blog.
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