Free online AAC to OMA converter

What the AAC format is

AAC, or Advanced Audio Coding, is a lossy audio codec commonly stored with the .aac, .m4a, or .mp4 extension. Apple Music and iTunes, smartphones, streaming platforms, cameras, and media applications use AAC because it normally provides smaller files than MP3 at a comparable bitrate.

A standalone .aac file usually contains an ADTS AAC stream. An .m4a file generally contains AAC inside an MPEG-4 container, so changing the filename extension does not convert it. FFmpeg, VLC, iTunes, Apple Music, and many recording or editing applications can create or decode AAC.

What the OMA format is

OMA is Sony's OpenMG Audio container, associated primarily with ATRAC3, ATRAC3plus, and ATRAC Advanced Lossless audio. SonicStage and older Sony Connect or Net MD workflows used .oma files for music transferred to compatible Walkman players and MiniDisc-related hardware.

OMA can contain OpenMG DRM. A DRM-protected file is tied to the software, account, or device that created it and cannot be made interchangeable simply by changing its extension. Non-protected OMA files may still require ATRAC support, which is absent from many current media players.

How to actually convert AAC to OMA

The most dependable desktop workflow is to decode AAC to WAV with FFmpeg, then import the WAV into Sony SonicStage or another application that can encode ATRAC and create OMA.

1. Install FFmpeg and place the source file in a working folder. For a stereo CD-quality intermediate, run ffmpeg -i input.aac -ar 44100 -ac 2 intermediate.wav. WAV avoids adding another compressed codec during the handoff.
2. Open SonicStage on a compatible Windows installation and import intermediate.wav. In the application’s audio or transfer settings, choose an ATRAC3 or ATRAC3plus encoding mode and the bitrate supported by the destination Sony device.
3. Use SonicStage’s library or device-transfer command to encode the imported WAV. The program normally creates an OMA file in its managed library, and may apply OpenMG protection when transferring it to a supported device.
4. Test the resulting file on the intended Sony player or in the same SonicStage installation. Do not assume that an OMA file produced by one program will work with every Sony model.

For a no-installation option, you can use the free AAC-to-OMA converter on 101convert.com. Upload the AAC file, select OMA as the output, start the conversion, and download the result. The service can only produce an OMA variant that its encoder supports; it cannot grant compatibility with DRM-restricted Sony software or hardware.

Quality, compatibility, and limitations

Converting AAC to OMA normally means decoding one lossy codec and encoding another, so it cannot restore discarded audio data. Use the original AAC bitrate as a guide, and avoid repeated conversions. A WAV intermediate prevents an additional lossy encode before ATRAC encoding but does not preserve information already removed from the AAC source.

Choose the sample rate and bitrate supported by the target device; older hardware may accept only specific ATRAC3 or ATRAC3plus profiles. OMA is not a universal audio format, and current Android, iOS, macOS, and Windows players may need a third-party decoder or conversion back to AAC, MP3, or WAV.

If the source AAC is protected by FairPlay or another DRM system, ordinary decoders may reject it. Only convert files that the software can legally and technically read. A renamed .aac file is not OMA, and an unprotected OMA file is not necessarily compatible with a player that expects Sony’s OpenMG licensing data.