What this audio converter does
Add MP3, WAV, M4A/AAC, FLAC, OGG Vorbis or Opus files and pick a target for each one. A typical batch might turn a folder of WAV takes from a recorder into MP3s for sharing, while a FLAC album becomes M4A for an iPhone.
The options panel (the slider icon) lets you choose the bitrate for MP3, M4A, OGG and Opus, resample to 48, 44.1, 32, 22.05 or 16 kHz, mix down to mono, and trim with a start and end time in seconds or minutes:seconds. Tags such as title and artist are carried across when the target format can store them.
Lossy or lossless?
WAV and FLAC are lossless: converting between them is bit-exact, and FLAC is simply WAV packed to roughly half the size. MP3, M4A (AAC), OGG and Opus throw away sound you are unlikely to hear in exchange for files about a tenth of the size. Each time you convert from one lossy format to another a little more detail is lost, so keep a WAV or FLAC master if you have one and make lossy copies from that.
As a rough guide: 128 kbps Opus or 160 kbps AAC is transparent for most listeners on music, MP3 needs about 192 kbps for the same result, and 64 kbps mono is plenty for speech, podcasts and voice notes.
How the conversion works
ConvertCove runs FFmpeg, the open-source engine behind most media software, compiled to WebAssembly. The engine (about 10 MB compressed) downloads the first time you convert an audio or video file and is cached by your browser afterwards. Your audio is read straight from disk into the tab and never sent to a server.