Why this is fast
MP4 and MOV sources stream-copy the video track (-c:v copy) and only re-encode the audio, so the heavy lifting is just the loudnorm + AAC pass — a fraction of the work of a full transcode. Uploads land at the nearest Backblaze B2 point of presence via a presigned URL, the encode runs server-side with native ffmpeg (real SIMD, threading, disk I/O), and the result comes back through Bunny CDN. A one-hour 1080p MP4 typically finishes in a few seconds end to end.
What this tool does, exactly
For MP4/MOV inputs, the command is ffmpeg -i input -c:v copy -af loudnorm=I=-16:TP=-1.5:LRA=11 -c:a aac -b:a 192k -movflags +faststart -f mp4 output.mp4. Video bytes pass through untouched, audio is normalized to integrated -16 LUFS with a true-peak limit at -1.5 dBTP and a loudness range of 11 LU. For WebM/MKV inputs (VP8/VP9 + Opus, which cannot be muxed into MP4), we add -c:v libx264 -preset veryfast -crf 20 -pix_fmt yuv420p so the output is still a clean, universally playable MP4.
EBU R128 vs peak normalization
Two completely different approaches. Peak normalization (the old way, still in basic editors) just scales the file so its loudest sample hits a target dB — a quiet track with one sharp peak ends up still feeling quiet because perceived loudness is mostly about average level, not peaks. EBU R128 (which we run) measures integrated loudness in LUFS — a perceptual unit weighted the way human ears actually hear — and adjusts the whole file so its average perceived loudness lands on target. That is why streaming platforms (Spotify, YouTube, Apple Podcasts) all standardized on LUFS-based normalization: it is the only measurement that makes everyone's uploads sit at the same comfortable level.
Loudness is not noise — pick the right tool
This tool fixes loudness. It does not remove hiss, fan hum, keyboard clatter, or room echo — in fact, turning a quiet track up will make any existing background noise more audible, not less. If the actual problem is a noisy room rather than a low level, run the audio through the background noise remover first, then normalize the cleaned audio. The two steps solve different problems and work best in that order.
Sister tools
Got hiss or hum, not just loudness? Remove background noise. Need just the audio out as MP3? Video to audio converter. Compress the leveled video for sharing? Video compressor. Cut the leveled video to a section? Video cutter. Check the mic level before the next take? Mic test. Capture a clean recording from the start with Clipy — the free screen recorder with mic-level guidance baked in.