Free online M4A to SND converter

Some older Unix, Sun, NeXT, embedded-audio, and specialist applications require an AU-style .snd file instead of .m4a. Converting the file lets those programs import, edit, or play the audio.

What the M4A format is

M4A is an MPEG-4 audio container commonly used for AAC-compressed audio and, less often, lossless ALAC audio. Apple devices, the Music app, iTunes, smartphones, voice-recording applications, and digital audio workstations commonly create it.

M4A files can contain metadata such as artist, album, title, artwork, and track information. AAC provides small files and good quality, but older software may not support the container or its codec.

What the SND format is

.snd is an ambiguous extension used by several historical sound formats. In a general audio conversion, it usually means the Sun/NeXT AU format, which has a simple header and can contain uncompressed PCM or companded audio such as μ-law.

AU/SND files remain useful with legacy Unix tools, older multimedia software, development environments, and embedded systems that expect an AU header. PCM is straightforward for older programs to decode, but it produces much larger files than AAC in an M4A container.

How to convert the file with FFmpeg

FFmpeg is suitable for repeatable conversions, batch processing, and precise control over the output. Install FFmpeg, open a terminal in the folder containing the source file, and run:

ffmpeg -i input.m4a -f au -c:a pcm_s16be output.snd

This creates an AU/SND file containing signed 16-bit, big-endian PCM while retaining the source sample rate and channel count. Replace the filenames with the actual names; quote paths containing spaces, for example "my recording.m4a".

For a broadly compatible mono file at 44.1 kHz, use:

ffmpeg -i input.m4a -f au -c:a pcm_s16be -ar 44100 -ac 1 output.snd

Some telephony and embedded applications require 8 kHz μ-law audio instead:

ffmpeg -i input.m4a -f au -c:a pcm_mulaw -ar 8000 -ac 1 output.snd

To convert without installing software, select the M4A file on 101convert.com, choose SND as the output format, start the conversion, and download the result. Test that file with the destination program because the .snd extension does not specify the internal codec or audio parameters.

Desktop conversion and required settings

Audacity can import M4A when its FFmpeg support is available. Open the file with File → Open, then use File → Export Audio and select Other uncompressed files. Choose AU (Sun/NeXT), then select the encoding required by the destination application, such as signed 16-bit PCM or μ-law. FFmpeg is preferable when exact sample format, byte order, or batch processing matters.

Before converting, check the receiving program’s requirements for the SND variant, codec, sample rate, bit depth, byte order, and channel count. An AU file with the correct extension can still fail if the application expects a different historical SND format.

Quality and compatibility limits

If the M4A contains AAC, conversion to PCM-based SND does not restore information removed by lossy compression. It decodes the AAC stream and writes the result in another representation; use the original lossless recording when available.

If the M4A contains ALAC with more than 16 bits per sample, exporting as 16-bit PCM reduces technical resolution. When supported by the destination software, preserve the source depth, for example:

ffmpeg -i input.m4a -f au -c:a pcm_s24be output.snd

PCM file size is approximately sample rate × bytes per sample × channel count × duration, excluding the small AU header. Conversion may also discard M4A-specific artwork and metadata, so retain the original M4A for archival use.