WAV is a thin container around uncompressed PCM samples, which is why a three minute song weighs thirty megabytes. Opus is the lossy encoding voice calls and browsers settled on, better than MP3 at the same bitrate and unreadable by most hardware players. ffmpeg sits between the two, and this page says exactly what happens to a WAV file on the way to becoming an OPUS one.
What runs when a WAV file becomes OPUS
ffmpeg held to a single thread, on a machine we rent and watch. Your WAV file is uploaded once, ffmpeg runs once, the OPUS comes back, and neither file is kept. WAV to OPUS is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the WAV into the OPUS
The running time and the channel layout. A stereo WAV comes back as a stereo OPUS of the same length: this is a re-encode, not an edit, and nothing here normalises, trims or boosts the WAV.
The whole of the WAV, start to end. OPUS is a lossy encoding, but it encodes all of the WAV rather than a shortened or quieter version of it, and the loudness you hear is the loudness you sent.
What WAV to OPUS costs you
Exactness, once and for good. The WAV holds every sample; OPUS keeps what its model believes you can hear and discards the rest. Going back from OPUS to WAV later rebuilds the file size and none of the sound, which is the single most common misunderstanding about this pair.
Album art, where the WAV carried any. ffmpeg passes -vn on every audio target here, which counts an embedded cover as a video stream and drops it along with the film it was never part of. That is deliberate rather than careless: keeping it makes the mux fail outright on several audio containers, and hiding the choice would be lying by omission.
Any hope of OPUS sounding better than the WAV. Nothing in this pass adds information, and a bitrate higher than the WAV deserved only makes a larger file of the same recording.
If a model is going to read the OPUS
An OPUS file is a waveform, and a language model reads text, so handing an assistant this OPUS directly gets you nothing. The OPUS becomes useful the moment somebody turns the sound into words, and that is a separate job with its own page here. WAV to OPUS is the step before it: get the sound out of the WAV in a container the transcriber accepts, then hand the model a transcript instead of a file it cannot open.
Running WAV to OPUS against the real engine with a real file, ffmpeg wrote 27,591 bytes of OPUS in 0.2 seconds, machine otherwise idle. That is one WAV file on one day and not an average, which is why the number is given together with the file that produced it.
The WAV to OPUS verdict was reached by ffprobe, meaning the container was actually demultiplexed, recognised under the right name, and carried at least one stream. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the OPUS file has anything inside it.
The same WAV file, sent somewhere else
Other outputs the probe measured out of a WAV file, so the cost of choosing OPUS can be read against something. Sizes do not compare across engines, because each family was probed with its own WAV witness file.
WAV to MP3: 24,468 bytes in 0.2 seconds, verified by ffprobe.
WAV to FLAC: 44,337 bytes in 0.1 seconds, verified by ffprobe.
WAV to OGG: 8,670 bytes in 0.1 seconds, verified by ffprobe.
WAV to M4A: 27,633 bytes in 0.2 seconds, verified by ffprobe.
WAV to AAC: 27,219 bytes in 0.2 seconds, verified by ffprobe.
WAV to WMA: 54,944 bytes in 0.1 seconds, verified by ffprobe.
Other ways into OPUS, and what they measured
Among the published routes into OPUS, WAV is the tenth largest output of the 16 measured. The witness files differ, so this ranks the probe run and not your document.
WEBM to OPUS: 26,907 bytes in 0.2 seconds.
WMA to OPUS: 25,770 bytes in 0.2 seconds.
WMV to OPUS: 25,770 bytes in 0.1 seconds.
MP4 to OPUS: 27,864 bytes in 0.2 seconds.
MP3 to OPUS: 27,107 bytes in 0.2 seconds.
What we will not pretend about WAV to OPUS
A WAV file over 150 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A WAV to OPUS run that passes 240 seconds is killed, and the ffmpeg process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
The WAV file behind the measurement on this page was a 3 second sine wave at 440 hertz, built by ffmpeg for the probe itself. That is why WAV to OPUS came out at 0.2 seconds, and it is not what your file will do. The measurement proves the pair works and says almost nothing about how long yours will take.
WAV to OPUS costs half a credit per conversion, whatever the length of the WAV. That is the same as an image or a document here, and it is a measurement rather than a gesture: an audio target on this engine is done in under two seconds, where a video target can take minutes.
A WAV longer than 60 minutes is refused before encoding. ffprobe measures the WAV first and answers with a refusal, rather than starting a job the 240 second guard would kill halfway to the OPUS.
WAV to OPUS waits at the audio door, which is 2 slots wide and gives up after 5 seconds rather than making you wait twenty times the length of the work. Until the 30th there was one door for everything, and a single video transcode starved every audio conversion for its whole duration: an OPUS that needed less than a second was answered with a refusal after twenty.
Nothing here reads what is inside the WAV. No transcription, no scene detection, no summary: WAV to OPUS is a container and codec operation, and the OPUS says exactly what the WAV said, in a different wrapper. The sound is the whole payload.
One WAV file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
WAV to OPUS: what people ask
What actually converts my WAV file to OPUS?
ffmpeg does it, held to a single thread, on a machine we rent and watch. Not a browser trick and not somebody else service: the WAV file is uploaded once, ffmpeg runs once, the OPUS comes back, and neither file is kept afterwards.
How long does WAV to OPUS take?
The probe measured 0.2 seconds for 27,591 bytes of OPUS, on a 3 second file. An audio target scales far better than a video one: three minutes of source through this engine takes under a second, because only the sound is encoded. Past 240 seconds any run is stopped, and an audio one does not get close.
What do I lose going from WAV to OPUS?
The one to know about first: Exactness, once and for good. The WAV holds every sample; OPUS keeps what its model believes you can hear and discards the rest. Going back from OPUS to WAV later rebuilds the file size and none of the sound, which is the single most common misunderstanding about this pair.
Will the OPUS sound better than the WAV?
No. Nothing in this pass adds information to the WAV, so the OPUS is at best an exact carry of what you sent and at worst one more lossy pass over it. Asking for a higher bitrate than the WAV deserved just makes a bigger file of the same recording.
Is WAV to OPUS free?
There is a free allowance every month, and one WAV to OPUS conversion costs half a credit against it however long the WAV runs. An audio target is charged per conversion and not per minute, because the engine encodes three minutes of sound in well under a second.