Why M4A files get rejected everywhere
M4A is AAC audio in an MP4 container — technically excellent, but car stereos, older software, some Android apps, transcription services and court/HR submission systems still want MP3. One decode, one high-quality encode, done locally.
FAQ
Voice memos from iPhone?
Yes — that's exactly what they are. AirDrop or transfer them over, drop them here. There's also a dedicated voice-notes page that additionally handles WhatsApp .opus and voicemail files.
Audiobook .m4b files?
They convert (drop them here), currently as one long MP3 — chapter splitting is on the workbench.
Quality?
At 128 kbps+, transparent for speech; use 192 for music.