Convert MP4 to M4A

A copy, not a conversion

MP4 and M4A are the same file format, MPEG-4. The only difference is that an M4A holds sound and nothing else. So when the sound inside your video is AAC, Octoolo does not decode and re-encode it: it lifts the AAC stream out and puts it in a new file. The M4A keeps the bit rate of the video's sound and sounds exactly like the video did, and it takes about as long as copying a file of that size.

Two things turn the copy into a real conversion. If the video's sound is something an M4A does not hold as it is, such as MP3 or AC-3, it is encoded as AAC: 256 kbps at High, 192 at Balanced, 128 at Small, or close to the original's rate with As it is. And any change under More settings, whether a new sample rate, channel count or bit rate, means the sound has to be made again.

Where M4A files play

M4A is at home on Apple devices: the iPhone, Apple Music and iTunes, and every Mac play it. So do Windows 10 and 11, Android phones and current browsers. It is a good choice for:

• Listening on an iPhone to a talk, a class or a performance you filmed.
• Keeping recordings small without the second round of compression an MP3 would add.
• Making a ringtone: an iPhone ringtone is AAC in the same kind of file with an .m4r ending, and the ringtone maker cuts one to 40 seconds and saves it that way.

Where M4A falls short is older gear. Some car stereos and portable players only take MP3; for those, use MP4 to MP3 instead. And if an M4A ever needs to become something else, M4A to MP3 and M4A to WAV take it from there.

AAC or Apple Lossless

More settings offers two sound codecs for M4A. Automatic (AAC) is the one to keep: with As it is, it is what makes the lossless copy possible. Apple Lossless stores sound with no loss at all, but it cannot improve sound that was already compressed. An Apple Lossless M4A made from AAC sound plays exactly the same and takes several times the space.

Apple Lossless earns its place when the video's sound was never compressed, as in footage from some cameras that record uncompressed sound. Then it keeps every detail in roughly half the room a WAV would need.

Surround sound stays as it is: AAC holds up to eight channels, so a 5.1 track remains 5.1. If the M4A is meant for earbuds, choose Stereo under Channels, knowing that this makes Octoolo encode the sound again rather than copy it.

The same copy from other videos

AAC is the usual sound of far more than MP4 files. iPhones record it into MOV files, most Android phones and Octoolo's own screen recorder into MP4, and plenty of MKVs carry it too. For all of them, M4A with As it is works the same way: the AAC stream is lifted out and copied, whatever the picture was.

That makes a folder of mixed videos quick to clear. Drop it on the window and Octoolo picks out every video in it, up to 500, and since a copy needs almost no processing, four run at once. Each finished line shows the new file's size next to the change in percent, which for an M4A is a fair measure of how much of the video was picture. The originals are never touched, and an M4A never replaces a file already there: it gets a number instead.