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Glossary · format

What is M4A?

M4A is an audio-only file format that wraps AAC-encoded audio in an MP4 container. It carries the same audio that's inside YouTube videos, iTunes downloads, and Apple Music files — usually at 128, 192, or 256 kbps. Direct copy of m4a from YouTube is lossless; converting m4a to MP3 always loses some quality.

Also called:aac · mp4 audio · apple lossless

YouTube's audio tracks are AAC, served in m4a containers. When you download "audio only" from a YouTube video, the cleanest result is the original m4a — the bytes have not been re-encoded since the upload.

Converting m4a to MP3 runs the audio through an extra round of lossy encoding. The MP3 will be larger than the source and worse-sounding; "320 kbps MP3" still sounds slightly worse than the source 128 kbps AAC because the conversion adds artifacts on top of the existing ones.

Use m4a directly when your destination supports it: every modern browser, every music app, iOS, Android, macOS, Windows 10+, and most smart speakers do. Convert to MP3 only when the destination explicitly rejects m4a (some old car stereos, hardware MP3 players from before ~2015).

Common questions

Is m4a better than MP3?
At equivalent bitrates, AAC (in m4a) sounds better than MP3 — the codec is newer and more efficient. For YouTube downloads, m4a is also a direct copy with zero re-encode loss; MP3 always involves a quality-degrading conversion.
Will m4a play in my car stereo?
Most cars from 2010 onward support m4a/AAC. Older or cheaper systems may only accept MP3. If unsure, MP3 has the widest compatibility but at a small quality cost.

Related terms

MP3

MP3 is the most widely supported audio format.

Codec

A codec is the algorithm that encodes (compresses) and decodes raw audio or video into a smaller stream.

Container (file format)

A container is the file format that wraps one or more audio and video streams into a single file.

Bitrate

Bitrate is the amount of data a video or audio stream carries per second, measured in bits per second (bps) or kilobits (kbps) and megabits (Mbps).

VidPickr is a free, browser-based YouTube downloader. Every term in this glossary either describes how YouTube delivers video or why your downloads behave the way they do. Try the downloader →