Free online AAC to M4R converter

An iPhone ringtone must use an MPEG-4 audio file with the .m4r extension, so a standalone .aac recording needs to be packaged or re-encoded before import. The conversion is also useful when software accepts M4R but not raw AAC files.

What the AAC format is

AAC, or Advanced Audio Coding, is a lossy audio codec used in smartphones, streaming services, Apple media software, and many editing applications. A standalone AAC file normally uses the .aac extension and may contain an ADTS stream; AAC audio can also be stored in .m4a or .mp4 containers. At similar perceived quality, AAC usually produces smaller files than uncompressed PCM audio.

What the M4R format is

M4R is an MPEG-4 audio file identified by the .m4r extension and used primarily for custom iPhone ringtones. It normally contains AAC audio in an MP4-family container. The format provides ringtone-oriented compatibility and metadata support; it does not improve sound quality and is not a separate audio codec.

Changing .aac to .m4r in a filename is not enough for a raw AAC file. The audio must be placed in a compatible MPEG-4 container, and it may need to be re-encoded. Renaming can work only when the source is already an appropriate MP4/M4A container with compatible audio.

How to convert AAC to M4R

Using 101convert.com

1. Open the AAC-to-M4R converter on 101convert.com.
2. Upload the source .aac file.
3. Select M4R as the output format.
4. Start the conversion and download the resulting .m4r file.
5. For an iPhone ringtone, trim the audio to 30 seconds or less if it exceeds that limit.

101convert.com performs the conversion for free without requiring installed software. Do not upload private or copyrighted audio unless the service’s file-handling terms and your rights to use the recording are acceptable.

Using FFmpeg

FFmpeg can decode the source and create an M4R-compatible MPEG-4 file in one command:

ffmpeg -i input.aac -t 30 -c:a aac -b:a 192k -f ipod output.m4r

Replace input.aac and output.m4r with the actual filenames. The -t 30 option limits the output to 30 seconds; remove it for a non-ringtone file that does not need the iPhone ringtone limit. The -f ipod option selects an MP4-family container suitable for Apple device media.

Re-encoding an already lossy AAC source can add compression artifacts. If the source stream is compatible with the MP4 container, try remuxing without re-encoding:

ffmpeg -i input.aac -t 30 -c:a copy -f ipod output.m4r

Use the re-encoding command if the copied version has an incorrect duration, will not open, or is rejected by the phone. When available, a lossless original is the best source for creating a new AAC ringtone.

Compatibility and transfer limits

Use an AAC audio track without DRM, keep the ringtone at 30 seconds or less, and retain the .m4r extension. A higher bitrate cannot restore detail already discarded by the source; 128–256 kbps AAC is generally sufficient for a short ringtone, but the source quality and encoder determine the result.

On macOS, connect the iPhone in Finder and add or drag the .m4r file to the device’s ringtone area when available. On Windows, use the Apple Devices app or iTunes version that supports ringtone syncing. If the file is not listed, verify that it contains AAC audio in an MPEG-4 container, is under 30 seconds, is not DRM-protected, and has not acquired a hidden double extension such as .m4r.m4a.