Why this is fast
Two reasons. Native server ffmpeg runs roughly 4–8x faster than browser WebAssembly on identical hardware, thanks to real SIMD, threading, and disk I/O. And the network round-trip is short: uploads land at the nearest Backblaze B2 point of presence via a presigned URL (a viewer in Bangalore is not pushing bytes through US-east), the encode runs server-side, and the finished MP3 comes back through Bunny CDN from the same edge. Most files finish in a second or two of CPU time.
What this tool does, exactly
We run ffmpeg -i input -vn -c:a libmp3lame -q:a 2 -f mp3 output.mp3. The -vn drops any video stream (some inputs carry album art), the LAME encoder re-encodes at VBR quality 2 (~190 kbps average), and the -f mp3 forces an MP3 container regardless of what the file extension would otherwise suggest. No custom sample-rate or channel changes, so a 48 kHz stereo WAV stays 48 kHz stereo MP3, and a 44.1 kHz mono Voice Memo stays 44.1 kHz mono MP3.
VBR vs CBR — why we ship VBR by default
Variable bitrate (VBR) allocates more bits to complex passages and fewer to silence, so a 60-minute podcast at VBR quality 2 is roughly the same file size as 192 kbps CBR but consistently sounds cleaner on the busy parts. CBR only wins in two narrow cases: broadcast streaming where bandwidth must be perfectly predictable, and very old hardware (1990s in-car CD changers, mostly) that mis-handles the VBR header. For everything heading to a podcast host, a phone, or a chat client, VBR is the right default. We pin to LAME's VBR quality 2 because every blind-listening sweep since 2007 (HydrogenAudio's 128/192 kbps tests in particular) puts it at the practical transparency floor for general audio.
Sister tools
Want MP3 plus WAV, M4A, and OGG output options? Audio converter has a format picker (MP3 ships today; WAV / M4A / OGG coming). Specifically converting an Apple file? M4A to MP3 converter is the focused version. Pulling audio out of a video instead? Video to audio converter and MP4 to MP3 converter both work. Trim the MP3 down? MP3 cutter. Shrink it for email? Compress audio.