Convert MP4 to M4A

That is not a simplification. M4A is the same ISO MPEG-4 container Apple introduced for audio in 2004, holding the same AAC that already sits inside the video file. Nothing structural changes between the two; a track is removed and the extension tells software to expect sound rather than a film.

Which is why this is the natural target for taking audio out of a video on an Apple device. The Music app files it correctly, the metadata fields are the ones an iTunes library already reads, and a phone decodes AAC in hardware without spending battery on it.

Because the source and the target both hold AAC, the audio could in principle be lifted out packet by packet and dropped into the new container without a decoder ever running. That is the fast, exact version of this operation, and it is the reason people choose M4A over MP3 in the first place.

This conversion page does not take that route: it decodes the AAC and encodes it again, which costs one generation. The Extract audio tool on this site does take it — choose M4A there and the original packets are copied across untouched. If an exact copy of the soundtrack matters, that is the page to use, and it is faster as well.

Less than the arithmetic suggests, and not nothing. The first encode, done when the video was made, is where most of the information went; a second pass at the balanced or high setting mostly reproduces what survived rather than removing another equivalent chunk. On speech it is inaudible by any ordinary test.

On music it is measurable, and on good headphones occasionally noticeable — particularly on cymbals, applause and other broadband sounds that lossy encoders find expensive. If the M4A is going into a library you intend to keep for years, that is the argument for using the lossless tool instead of this page.

M4A is the better format on the merits. AAC reaches the same perceived quality as MP3 in fewer bits, it handles high frequencies more gracefully, and it is what every streaming service and every phone actually uses behind the scenes. On a phone, a computer or a tablet it is the right answer without qualification.

MP3 wins on one axis and it is a big one: it plays on absolutely everything, including car stereos from 2004, gym equipment, hi-fi separates and cheap MP3 players still in drawers. The test is whether you can name the device. If you can and it was made this century, choose M4A. If the file is going somewhere unknown, choose MP3.

Roughly a megabyte a minute at the balanced setting, so a forty-minute talk lands near forty megabytes and a three-hour audiobook chapter near a hundred and eighty. The size of the video it came from barely enters into it — a 300 MB recording and a 3 GB recording of the same lecture produce nearly the same M4A, because the difference between them was entirely picture.

The quality band moves that figure by about a factor of two in each direction. The small setting is right for speech going onto a phone with limited storage; the high setting is for music, where the extra bytes are buying something you can hear.

Apple Lossless files are also called .m4a, and this is the single most common misunderstanding about the format. ALAC keeps every sample exactly; AAC does not. Two files with the same extension can therefore be lossless or lossy with nothing in the name to tell them apart.

What this page writes is AAC. That is the correct choice and not a compromise, because the audio inside an MP4 was already lossy AAC — there is no lossless original hiding in the file for ALAC to preserve. Encoding it as ALAC would produce a much larger file containing exactly the same audible content.

The container has proper fields for artist, album, title, track number and artwork, which is a real advantage over some audio formats and the reason Apple libraries sort M4A files cleanly. This conversion leaves them empty, because the video it came from usually had nothing meaningful to copy in.

Setting them is worth the minute it takes if the file is joining a library, and it is best done once, before the file is copied to a phone. A tagging tool, or the info panel in the Music app, both do the job; a converter guessing an artist from a file name does not.

Up to a hundred files at a time on the free tier, each converting on its own with its own progress, and the finished results downloadable together as a ZIP. Nothing is queued behind anybody else because there is no shared server involved.

This is where running in the browser stops being a privacy point and becomes a practical one. A term of lecture recordings through a hosted converter means a term of uploads and a daily allowance to run out of; here it means leaving a tab open while the machine works.

The decode and encode happen inside the browser tab on your own processor. You can confirm it by opening the network tab and converting something: nothing carrying the video is sent. The free tier takes files up to 100 MB.

For this pair it is the material that makes it matter. The videos people pull audio out of are lectures, sermons, interviews, therapy sessions, band practices and family occasions — the kind of recording where the safest handling is not to hand it to a company you have never heard of in exchange for a file you could have made locally.