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How to convert a WAV to M4A on a Mac and save space

· 6 min read

A WAV file is uncompressed audio, so a recording of any length takes up a lot of space. Converting it to M4A makes it far smaller and plays in Music, on an iPhone and in QuickTime Player. The trade is that a normal M4A is lossy, so keep the WAV if it is a master recording.

Why a WAV is so large

WAV stores audio sample by sample with no compression. That is ideal for editing and archiving, because nothing is thrown away, but it adds up quickly. A few minutes of stereo audio can run to tens of megabytes, and an hour-long interview or lecture can reach hundreds of megabytes.

M4A is a compressed container that Apple’s apps are built around. Most M4A files use AAC, which discards detail you are unlikely to hear, so the file is a fraction of the WAV’s size. That makes it a good fit for email, messaging, voice memos and music players. If the problem is sending the result somewhere, how to make an audio file smaller to email from a Mac goes deeper.

Decide whether you can afford the loss

For speech, such as interviews, meetings and lectures, a lossy M4A is almost always fine, and the saving is large. For music you care about, or a recording you may edit later, keep the WAV as your master and convert a copy.

There is also a lossless kind of M4A, called Apple Lossless, which shrinks the file without losing detail. It is smaller than a WAV but not nearly as small as AAC. If you want to save some space with no loss at all, that is the option to look for. Lossy versus lossless: what you lose when you convert a file explains the difference.

Option 1: Convert with Manatee

Manatee reads WAV and writes M4A, working entirely on your Mac with nothing uploaded. Its conversion engine is built in, so there is nothing else to download.

  1. Open Manatee and choose Convert.
  2. Drop your WAV files into the window, or onto the menu bar icon. Several at once is fine.
  3. Choose M4A as the target.
  4. The M4A is saved beside the WAV. The original is never modified.

Compare the sizes in Finder when it finishes. If the M4A is about the same size as the WAV, check it with Command-I, as that suggests it is not the compressed kind you were after. Manatee is free for 24 hours with every feature, then $9 once.

Option 2: Convert in Finder

macOS has a built-in way to convert audio files without any extra software.

  1. Select one or more WAV files in Finder.
  2. Control-click, or right-click, and look for Encode Selected Audio Files in the menu.
  3. Choose a setting, such as High Quality or a specific bitrate, and confirm.
  4. The converted files appear in the same folder.

This is quick for a handful of files. The options are limited, and the menu item may not appear for every file. If it is missing, try another route.

Option 3: Convert in Terminal

macOS includes a command called afconvert that does this directly:

afconvert -f m4af -d aac -b 192000 input.wav output.m4a

The -b 192000 sets the bitrate in bits per second. For speech, 96000 is often plenty; for music, 192000 or 256000 is a safer choice. To do a whole folder:

for f in *.wav; do afconvert -f m4af -d aac -b 192000 "$f" "${f%.wav}.m4a"; done

This is built into macOS, so nothing needs installing, but you handle the naming and any failures yourself.

Check the result

  1. Play the beginning, middle and end of the M4A. A file that stops short may mean the WAV itself was cut off.
  2. Make sure the sound is not speeded up or pitched high. That points to a sample rate issue; an audio file that plays too fast or sounds high-pitched explains it.
  3. Drag one file into Music and confirm it plays and shows up correctly.
  4. Keep the WAV until you are satisfied, then decide whether you still need it.

A WAV that will not play at all is a different problem, covered in a WAV file that will not play on a Mac.

Questions

How much smaller will the M4A be? A lossy M4A is typically several times smaller than the WAV, depending on the bitrate you choose. Compare the two in Finder to see the actual saving for your file.

Is the quality noticeably worse? For speech, usually not. For music, a higher bitrate keeps more detail, and most people find a good setting hard to tell from the original on everyday speakers.

Does converting delete my WAV? No. The M4A is a new file next to the original, and the WAV stays exactly as it was.