Audio Engineering

Opus, AAC and MP3: Which Audio Format Fits Your Device

A plain comparison of the three codecs you meet on YouTube, and why the most compatible format is not always the best sounding one.

7 min read · Published 17 August 2026 · Updated 17 August 2026

MP3Juice
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Audio waveforms and format labels on a computer screen

Three codecs cover most of the audio you meet online. MP3 is the old standard, AAC is the format Apple helped popularise and Opus is the modern default for the web. They all remove data to make files smaller. They do it in different ways and with different results.

Three codecs, three eras

Feature	MP3	AAC	Opus
First released	1993	1997	2012
Efficiency	Baseline	Better than MP3 at the same bitrate	Better than both at low and mid bitrates
YouTube use	Not used	MP4 streams, around 128kbps	WebM streams, around 160kbps
Device support	Almost everywhere	Apple, Android and most modern players	Modern phones and computers, fewer car stereos

Why YouTube uses Opus and AAC

Google serves an enormous number of hours every day. A small reduction in bitrate across all of them saves a lot of bandwidth. Opus was designed for the web and keeps speech and music intelligible at low bitrates. AAC does a similar job for devices that expect an MP4 container, which includes iPhones and Safari.

MP3 is not part of that pipeline. It is older and less efficient, so it would cost more bandwidth for the same perceived quality. YouTube has no reason to use it internally.

What a converter does

The conversion is a lossy to lossy step. The source is decoded to raw samples and encoded again in the target format. The second encode cannot restore what the first one removed. A good encoder can keep the loss small, but it cannot make the file better than the stream it started from.

This is why a 320kbps MP3 from a 160kbps Opus source sounds like the source. The encoder is filling space, not adding detail. The result is still useful because MP3 plays on devices that ignore WebM.

Which format to choose

MP3. Pick it for a car USB drive, an older MP3 player, a cheap Bluetooth speaker or a device whose manual does not mention other formats. Compatibility is the reason to accept the older codec.
MP4 with AAC. Useful when you want video and audio together, or when the file is going straight into an Apple app that prefers AAC.
Opus. The better choice for storage and quality on a modern phone or computer, if your player supports it. VLC does. Many car stereos do not.

What about FLAC

FLAC is lossless, so it preserves everything in the source. Converting a lossy Opus stream to FLAC does not make it lossless. It only wraps the same limited audio in a larger container. FLAC makes sense when the original is a CD rip or a lossless download, not when the source is a streaming platform.

Listening tests beat spec sheets

A codec comparison table tells you what should happen in a lab. Your ears and your equipment decide what actually matters. Test one track you know well on the headphones or speaker you use every day. If you cannot hear a difference, choose the smaller file and keep the space.

The short version

MP3 is the safe choice for old hardware. AAC fits Apple devices and MP4 video. Opus is the efficient modern option when your player supports it. None of them can improve the source, so pick the format your device needs and leave the bitrate at a sensible level.