BTR AMP
M4A is the MPEG-4 audio container — usually holding AAC, sometimes ALAC — and it comes with siblings: M4B for audiobooks and plain MP4 audio. Most iTunes-era collections are built from this family.
Why the built-in Music app isn't enough
iOS plays M4A natively, but the built-in app imposes its own structure: fixed navigation, no on-device tag editing, and slowdowns as the library grows. Audiobooks in M4B are handled as an afterthought in music-first apps generally — long files need remembered positions, speed control, and their own place in the library, not a spot in the songs list.
How BTR AMP plays M4A
BTR AMP plays the whole family — M4A, M4B, and MP4 audio — with the exact codec shown per track and the on-device editor covering MP4/iTunes tags. Audiobooks and podcasts get dedicated media types with their own filtering and sorting, an In Progress view, and one-tap resume that picks up where you left off; variable speed from 0.5× to 2× and a sleep timer round out long-session listening. Music in M4A sits in the same library as MP3, FLAC, and every other supported format, organized by custom tabs and smart playlists.
Getting your M4A files onto your iPhone
M4A, M4B, and MP4 files transfer like everything else.
Send files over Wi-Fi from any browser on your computer (Connect → Wi-Fi Transfer), pull them from Google Drive, OneDrive, iCloud Drive, an SMB share, or WebDAV, use AirDrop, or play straight from a USB drive. The transfer guide walks through each method, and the importing guide covers the details.