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OPUS
What is an OPUS file?
The best-sounding format at low bitrates. What voice messages and calls use.
What OPUS is
OPUS is a codec: the encoding itself rather than the box it travels in. It is used for streaming and the web.
The extension is .opus, and the full name is Opus Audio. Both matter less than what the file can hold, which is what the rest of this page is about.
Where OPUS came from
Xiph.Org published it in 2012. The specification is RFC 6716.
Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.
The specification is public
Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.
Detail is traded for size
OPUS discards detail to stay small, and what it discards does not come back. That is the right trade for something being looked at and the wrong one for something being edited: each re-save takes another bite.
What else it can carry
OPUS can hold a layout that lets it start playing before it has finished arriving.
That matters mostly when converting: whatever the target cannot hold is dropped, usually without a warning.
How many audio channels
Up to 255. Two covers stereo and is what almost everything is; more than two is surround, and it is the part most likely to be folded down when converting to a format that does not define it.
What opens OPUS
VLC, FFmpeg and Audacity read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
Current browsers read it; older ones do not.
Where support is uneven, serving a second format alongside it is the usual answer — the browser takes the one it understands and nobody is left out.
It is a delivery format
OPUS is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
What goes wrong with it
The recurring complaints: support outside its home ground is uneven.
None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.
The facts, in one place
| Extension | .opus |
|---|---|
| Media type | audio/opus |
| Published by | Xiph.Org |
| First published | 2012 |
| Specification | RFC 6716 |