Add your AAC file
Drop one or more .aac files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
AAC to OPUS
Re-encoding .aac audio as .opus changes how the sound is compressed and which players will accept it. Free, private, and validated — the file never leaves your browser.
100% private for supported formats
Runs on your deviceConvert supported files
Drop AAC files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting AAC audio to Opus audio
Re-encoding .aac audio as .opus changes how the sound is compressed and which players will accept it. An .aac file holds raw Advanced Audio Coding data, usually as an ADTS stream. AAC was designed as MP3's successor and delivers audibly better quality at the same bitrate, though the bare .aac extension is rarer than AAC audio traveling inside .m4a or .mp4 files.
An .opus file contains audio compressed with the Opus codec, stored in an Ogg container. Opus represents the current state of the art in lossy audio, beating MP3, AAC, and Vorbis in listening tests at nearly every bitrate from whisper-thin speech settings up to transparent music encoding. For this route the practical draw is best-in-class efficiency at essentially every bitrate and royalty-free with an open reference implementation — balanced against older car stereos, AV receivers, and MP3 players have never heard of it, which is worth knowing before you commit a large batch.
Why convert AAC to OPUS?
The practical trigger for this conversion is usually a mismatch: with .aac, raw ADTS files handle tags and cover art poorly. Switching to .opus buys you best-in-class efficiency at essentially every bitrate, which is why it is the better fit for compressing podcast and voice-chat audio to tiny files. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
AAC vs OPUS at a glance
| Aspect | AAC audio (.aac) | Opus audio (.opus) |
|---|---|---|
| Format type | Lossy — discards detail it judges invisible to shrink files | Lossy — discards detail it judges invisible to shrink files |
| How it stores data | a pure MDCT transform codec, free of the hybrid filterbank compromise that limited MP3 | the hybrid SILK/CELT design switches coding modes automatically based on content |
| Strongest at | receiving the audio track copied out of MP4 video without re-encoding | compressing podcast and voice-chat audio to tiny files |
| Weak spot | raw ADTS files handle tags and cover art poorly | older car stereos, AV receivers, and MP3 players have never heard of it |
| Metadata | no standard tag container exists for raw ADTS streams; ID3 tags are sometimes prepended but poorly supported, so wrapping in .m4a is the reliable way to tag AAC | vorbis comments in the OpusTags header, including cover art via METADATA_BLOCK_PICTURE, plus an output-gain field used for loudness normalization |
Pick OPUS as the output
Select .opus in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if OPUS is selectable, the route is real and validated.
Convert on your device
Press Convert. The transcode runs on an FFmpeg engine compiled to WebAssembly, so the audio never leaves your device.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid OPUS file. Outputs keep the original filename with the .opus extension.
AAC to OPUS questions, answered
Will converting AAC to OPUS lose quality?
A second lossy step always costs a little, because aac is lossy-oriented and opus is lossy-oriented and each encoder discards detail differently (generation loss). At the default quality the difference is rarely visible; avoid repeated round-trips between .aac and .opus.
Is it private to convert AAC files here?
Yes — the .aac file is processed inside your browser tab and never uploaded. The transcode runs on an FFmpeg engine compiled to WebAssembly, so the audio never leaves your device. Close the tab and the file is gone from memory.
Where will the OPUS file work?
Chrome, Firefox, and Edge have played Opus for a decade and Android supports it natively, while Safari initially accepted the codec only inside CAF or WebM wrappers before extending support to .opus files. Legacy hardware such as older car head units remains the real gap, and conversion to MP3 or AAC bridges it.
Will the OPUS file be bigger or smaller than my AAC?
It depends on the content: the hybrid SILK/CELT design switches coding modes automatically based on content. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my AAC file?
This converter strips container metadata deliberately (the FFmpeg command runs with metadata mapping disabled) so exported files do not leak recording details. In the source, no standard tag container exists for raw ADTS streams; ID3 tags are sometimes prepended but poorly supported, so wrapping in .m4a is the reliable way to tag AAC; none of it is transmitted anywhere because the file never leaves your browser.
Can I convert OPUS back to AAC?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .aac → .opus → .aac is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.