Free online M4A to AT3 converter

What the M4A format is

M4A is an MPEG-4 audio container, usually carrying AAC audio and sometimes Apple Lossless Audio Codec (ALAC) audio. AAC-based M4A files are lossy and are commonly created by Apple Music, iTunes, smartphones, media players, and audio editors; ALAC-based files preserve the source audio without lossy compression. M4A files may also contain metadata such as title, artist, album, artwork, and chapter information.

What the AT3 format is

AT3 is an audio file extension associated with Sony ATRAC3 compression. It was used in Sony software, portable players, and PlayStation Portable-related media workflows. ATRAC3 produces smaller files than uncompressed PCM audio and supports several fixed bitrate modes, but it is a lossy codec with much less support on current computers and phones than AAC or MP3.

Use AT3 only when the target Sony application or device specifically requires it. An AT3 file may not work merely because its filename ends in .at3; the encoder, ATRAC3 profile, bitrate, sample rate, channel layout, and container structure must also match the target software.

How to convert M4A to AT3

Using the built-in online converter

1. Open the M4A-to-AT3 converter on 101convert.com.
2. Upload the source .m4a file.
3. Choose AT3 as the output format and start the conversion.
4. Download the resulting .at3 file and test it in the intended Sony application or device.

This option requires no installed software and is available free on the 101convert.com website. Do not use it for recordings that cannot be uploaded to a third-party processing service.

Using desktop software

Desktop conversion is normally a two-stage process because general-purpose audio tools can decode M4A more readily than they can encode Sony ATRAC3.

1. Decode the M4A to an uncompressed WAV file with FFmpeg:

ffmpeg -i input.m4a -ar 44100 -ac 2 intermediate.wav

The command creates 44.1 kHz stereo PCM, a common input format for ATRAC3 encoders. If the target device specifies another sample rate, channel count, or bitrate, follow that device's specification instead.

2. Open intermediate.wav in Sony Sound Forge or another desktop program that includes an ATRAC3 encoder.
3. Choose the ATRAC3 export function, commonly under File → Save As or File → Render As, then select the required ATRAC3 bitrate and .at3 output.
4. Copy the generated file to the target device using the directory and naming rules required by that device.

FFmpeg is useful for the M4A-to-WAV stage, but its installed build may not include an ATRAC3 encoder. If the export dialog does not list ATRAC3, use an encoder supplied by Sony software or a dedicated ATRAC3-capable application rather than renaming the WAV file.

Quality and compatibility limitations

Converting AAC M4A to ATRAC3 decodes one lossy format and encodes another, so it cannot restore discarded detail. Converting ALAC M4A avoids an additional loss during the source decode, but the ATRAC3 output is still lossy. Keep the original M4A as the archival copy.

AT3 compatibility is stricter than the extension suggests. Older Sony hardware may accept only particular ATRAC3 bitrates, usually at 44.1 kHz, and may reject files with unsupported stereo settings, metadata, or container variants. Test a short converted file before processing a large library, and verify playback on the actual target device rather than relying only on a desktop media player.