Audio file formats vs Bluetooth codecs
The format stored on your phone and the codec used to send sound to headphones are separate choices.
What is a Bluetooth codec?
A Bluetooth audio codec represents sound for transmission between devices. A file codec represents the audio stored in your music file. The same name, such as AAC, can appear in both contexts without proving that the compressed file is sent unchanged.
The playback app decodes the source, and the output path may mix, adjust and encode audio for the wireless connection. Do not assume AAC files avoid re-encoding merely because the headphones also use AAC.
Will FLAC or ALAC make Bluetooth lossless?
Not by itself. Lossless describes preservation in the source file. If the wireless link uses a lossy codec, that stage applies compression even though the source is lossless. Apple documents AAC Bluetooth use for a range of its wireless headphones, and identifies specific supported connections for lossless playback. Check the exact product and connection; do not generalise one capability to every AirPods model.
Should I change my music files?
Keep lossless originals if you want an archive or use wired playback too. Use compact listening copies when phone storage matters. Keep existing good MP3 or AAC files rather than repeatedly converting them between lossy formats.
Your phone and headphones must support a compatible transport codec. A file extension does not force that selection. For the broader terminology, see Bluetooth audio codecs explained.
What should I check first?
- Identify the source file codec, rather than relying on the extension.
- Check which output connection you are using: Bluetooth, wired analogue or USB audio.
- Check the capabilities of the exact phone, headphones and playback app.
- Resolve dropouts, volume and fit before assuming a different source format will fix the sound.
For local iPhone files, see playing music without iTunes.
Sources
Reviewed 7 October 2026.