Convert AAC to OPUS Online
Convert AAC audio to Opus for Discord, VoIP, and efficient distribution.
.aac, .m4a · up to 100 MB
What it's for
Apple library to Opus: smaller size, greater efficiency
Half the bitrate, same quality
Opus at 64 kbps outperforms AAC at 128 kbps in perceptual quality per Xiph.org MUSHRA studies (2012).
Native Discord and WebRTC
Opus is the mandatory audio codec in WebRTC (RFC 7874). Files in Discord and Telegram's native format.
100% private
Your audio library is never uploaded to any server. Local processing with FFmpeg.wasm.
Royalty-free
Opus is patent and royalty free. Distribute without license restrictions, unlike AAC.
How it works
Three steps, no hassle
Upload your AAC or M4A file
Drag or select your .aac or .m4a file from iTunes, Apple Music, or any source. Up to 200 MB.
Conversion to Opus
FFmpeg.wasm transcodes AAC to Opus directly in your browser. No servers.
Download your Opus file
Get your .opus file optimized for Discord, WebRTC apps, streaming, or efficient storage.
FAQ
Got questions?
Yes, and this is the primary technical reason to convert AAC to Opus. Xiph.org's perceptual evaluation studies published in 2012 using the MUSHRA protocol (ITU-R BS.1534) demonstrated that Opus at 64 kbps significantly outperforms AAC-LC at 64 kbps in perceptual quality. At 96 kbps, Opus matches or exceeds AAC-LC at 128 kbps. This advantage is especially pronounced in the 32–96 kbps range relevant to voice transmission, low-bitrate podcasts, and storage on space-limited devices.
Yes, it is a lossy-to-lossy transcode: AAC is decoded to PCM and re-encoded to Opus, adding a second generation of loss. To minimize the impact, use an Opus bitrate equal to or higher than the original AAC bitrate. If the original AAC is at 128 kbps, encode the Opus at 128 kbps or more. The conversion does not restore frequencies discarded by the original AAC encoder. The net benefit is the codec change for greater future efficiency, not an immediate quality gain.
Discord chose Opus for three technical reasons: latency (Opus has configurable algorithmic latency of 2.5 to 20 ms, AAC-LC has a minimum latency of ~45 ms due to the 1024-sample frame size at 44.1 kHz); efficiency at low bitrates (Opus is superior to AAC at 32–64 kbps, the voice range); and licensing (Opus is royalty-free, AAC requires license payments to Via Licensing). WebRTC platforms are defined in W3C and IETF standards with Opus as the mandatory audio codec (RFC 7874, May 2016).
Technically yes, though there are copyright considerations: files purchased from the iTunes Store or Apple Music with DRM (FairPlay) cannot be converted with this tool because they cannot be decoded without authorization. DRM-free purchases (iTunes Plus, since 2009) and CDs ripped to AAC by the user can be converted. The DRM-free .m4a file is opened, FFmpeg decodes the AAC, and encodes to Opus.
For voice audio, Opus at 64–96 kbps offers quality equivalent to AAC at 128 kbps. For music, Opus at 96–128 kbps is perceptually equivalent to AAC at 128–160 kbps according to the 2012 MUSHRA studies. In short: you can use half the bitrate in Opus and get similar or better quality, resulting in files 30–50% smaller than the original AAC if you lower the bitrate, or the same quality at the same bitrate with Opus as a more modern codec.
Yes. Opus in OGG container (.opus) is supported by: VLC (since 2.1, 2013), mpv, ffplay, foobar2000 with Opus component, Audacious, MusicBee, Deadbeef, Firefox (since v15, 2012), Chrome (since v25, 2013), and hardware players with firmware updated post-2015. Spotify has used Opus for streaming since 2014. YouTube uses Opus in WebM containers for its low-latency audio streams.
Convert AAC to Opus: Apple library for Discord, VoIP, and efficient streaming
AAC (Advanced Audio Coding) was standardized in ISO 13818-7 in 1997 as the technical successor to MP3. Apple adopted AAC as its iTunes Store distribution format in 2003, at 99 cents per song at 128 kbps without DRM (iTunes Plus, since 2009). Apple Music distributes its catalog at 256 kbps AAC-LC, and iTunes Plus purchases are fully portable DRM-free M4A files. The music library of millions of Apple users is in AAC format, an excellent codec for its time but designed before the current needs of low-latency streaming, VoIP communications, and low-bitrate podcast distribution became priorities. Opus, standardized in RFC 6716 of September 2012 by IETF and Xiph.org, was explicitly designed to cover all those needs that AAC did not optimize: configurable algorithmic latency from 2.5 to 60 ms (AAC-LC has a fixed minimum latency of ~45 ms), superior efficiency at 32–96 kbps for voice and music, and no royalties (AAC requires license payments to Via Licensing for commercial implementations, while Opus is completely royalty-free per the IETF patent policy). Converting an AAC library to Opus makes sense specifically when the destination is platforms that use Opus natively: Discord, where all audio clips are transmitted in Opus; WebRTC applications defined in RFC 7874 (May 2016) that specify Opus as the mandatory audio codec; and personal archiving where you want to maximize storage efficiency while maintaining perceptual quality.
The technical comparison between AAC-LC and Opus has been rigorously documented in Xiph.org's perceptual evaluation studies conducted in 2012 using the MUSHRA protocol (MUltiple Stimuli with Hidden Reference and Anchor, defined in ITU-R BS.1534) with a trained listener panel and test material representative of multiple musical genres. Results showed that Opus at 64 kbps achieved MUSHRA scores significantly higher than AAC-LC at 64 kbps, and that Opus at 96 kbps achieved scores equivalent to AAC-LC at 128 kbps. At high bitrates (192 kbps and above), AAC-LC and Opus have comparable performance and both achieve perceptual transparency with most test material. Opus's advantage over AAC is most pronounced at low bitrates because Opus uses the SILK codec for voice (specifically optimized for the characteristics of the human voice) and the CELT codec for complex tones, with dynamic switching between them. AAC-LC uses MDCT at a fixed frame length of 1024 samples, which is not optimal for voice at low bitrates. For converting AAC libraries to Opus with a size-reduction objective: a 256 kbps AAC file of 1 hour of music can be converted to Opus at 128 kbps with perceptually equivalent quality, resulting in a file 50% smaller. For 128 kbps AAC files intended for streaming or podcasting, Opus at 96 kbps offers comparable quality with 25% less size.
Convertir.ai performs the AAC to Opus conversion entirely in the browser with FFmpeg.wasm. The process decodes the AAC (whether in an M4A container, MP4 container, or raw AAC stream) with FFmpeg's AAC decoder to 44.1 kHz or 48 kHz PCM, applies if necessary a resample to 48 kHz (the native sample rate of Opus per RFC 6716) using FFmpeg's Kaiser-windowed sinc filter, and encodes with libopus at the user-selected bitrate using the music application mode for quality audio or speech mode for voice. The output container is OGG with a .opus extension, the standard for distributing Opus outside of WebM containers. iTunes metadata from the original M4A file (©nam, ©ART, ©alb, ©day, trkn, ©gen) are converted to Opus Vorbis Comment format (TITLE, ARTIST, ALBUM, DATE, TRACKNUMBER, GENRE) for compatibility with players that read Vorbis tags. If the M4A includes album artwork in the covr atom, it is transferred to the Opus as METADATA_BLOCK_PICTURE so compatible players display it. M4A files with Apple FairPlay DRM protection cannot be processed, as the DRM prevents audio decoding by third-party software. iTunes Plus files (DRM-free, purchases since 2009) and user-ripped files are fully compatible. Processing occurs entirely locally: no audio file is sent to external servers. The service is free, with no file limit, no signup, and no watermark.