Free online AAC to OPUS converter

A media player, voice application, or browser project may require an Ogg Opus file instead of AAC. Conversion can also reduce size for speech or streaming, but it re-encodes already compressed audio and may reduce quality.

What the AAC format is

AAC (Advanced Audio Coding) is a lossy audio codec used by Apple Music, iTunes, YouTube, smartphones, digital broadcasting, podcasts, and many video files. AAC audio is commonly stored in .m4a or .mp4 containers; a standalone AAC stream usually uses the .aac extension and ADTS framing. The extension identifies the container or stream packaging, not always the codec by itself.

What the Opus format is

Opus is a lossy codec standardized by the IETF for internet audio, voice chat, video conferencing, games, podcasts, and other interactive applications. It is normally stored in an Ogg container with the .opus extension.

Opus handles speech and full-range music in one codec, supports low-delay applications, and can provide good quality at relatively low bitrates. Speech often works at approximately 24–64 kbps, while music commonly uses about 96–160 kbps; the correct setting depends on the source and target application. Support is strongest in current browsers and desktop or mobile software, while older hardware players may not recognize it.

How to convert the file

The conversion decodes the AAC stream and encodes a new Opus stream. It is not a codec copy: AAC and Opus are different codecs, so -c:a copy cannot produce an Opus file.

For a local conversion, install a current FFmpeg build, open a terminal in the folder containing the source, and run:

ffmpeg -i input.aac -c:a libopus -b:a 128k output.opus

Use the actual container filename when the AAC track is inside an M4A file:

ffmpeg -i input.m4a -c:a libopus -b:a 128k output.opus

The output.opus extension selects the Ogg Opus output. Replace 128k with the required bitrate; 48k or 64k is often adequate for speech, and 96k to 160k is a common range for music. FFmpeg normally preserves a compatible sample rate automatically. To copy metadata when the source contains transferable tags, add:

ffmpeg -i input.m4a -map_metadata 0 -c:a libopus -b:a 128k output.opus

You can also convert the file for free on 101convert.com without installing software: upload the AAC or M4A file, select OPUS as the output format, start the conversion, and download the resulting .opus file. Do not upload private recordings unless the service’s storage and processing policies are acceptable.

Quality and compatibility limits

AAC-to-Opus conversion is a lossy-to-lossy transcode. Opus cannot restore detail discarded during AAC encoding, and converting repeatedly between lossy codecs compounds quality loss. Use the original WAV, FLAC, or other lossless source when available.

Opus may produce a smaller file than AAC at a comparable perceived quality, but the result is not guaranteed to be smaller because bitrate, encoder settings, channels, and source content determine the size. Test the output in the destination application, especially on older devices.

Album artwork, chapter information, gapless-playback data, and custom tags may not transfer consistently from M4A or other AAC containers to Ogg Opus. Confirm those fields after conversion if they are needed.