Koldflux extract-audio test log, run 2026-10-21. ffmpeg/ffprobe: ffmpeg version 6.1.1-3ubuntu5 Copyright (c) 2000-2023 the FFmpeg developers
Browser runs: headless Chromium (Playwright, CSP bypass because the dev build needs eval) on next dev --webpack, pages /tools/convert/video-to-audio/mp4-to-mp3, mp4-to-wav, mp4-to-aac; buttons Choose file, Convert to X, Download X.
Note: figures for the 30 second size table and the 30.000181 s MP3 length come from an earlier session on a generated 30 s file; its log was not kept, so those rows are not reproducible from this file.

## ffprobe of the sample
ffprobe -v error -show_entries stream=codec_name,sample_rate,channels,bit_rate -show_entries format=duration,size -of default=nw=1 test-10s.mp4
codec_name=h264
bit_rate=107474
codec_name=aac
sample_rate=44100
channels=2
bit_rate=127710
duration=10.000000
size=300872
## ffprobe -show_entries format=duration,size of each file
out.mp3:
codec_name=mp3
sample_rate=44100
channels=2
bit_rate=128000
duration=10.057143
size=161270
out.wav:
codec_name=pcm_s16le
sample_rate=44100
channels=2
bit_rate=1411200
duration=10.007800
size=1765454
out.aac:
codec_name=aac
sample_rate=44100
channels=2
bit_rate=125906
duration=10.357632
size=163011
c.mp3:
codec_name=mp3
sample_rate=44100
channels=2
bit_rate=128000
duration=10.057143
size=161479
c.wav:
codec_name=pcm_s16le
sample_rate=44100
channels=2
bit_rate=1411200
duration=10.007800
size=1765454
c.m4a:
codec_name=aac
sample_rate=44100
channels=2
bit_rate=127710
duration=10.000000
size=162544
(out.* = browser downloads, c.* = command line)

## Commands for c.*
ffmpeg -i test-10s.mp4 -vn -c:a libmp3lame -b:a 128k c.mp3 ; ffmpeg -i test-10s.mp4 -vn -c:a pcm_s16le c.wav ; ffmpeg -i test-10s.mp4 -vn -c:a copy c.m4a

## volumedetect (ffmpeg -i FILE -af volumedetect -f null -)
/mnt/koldflux-build/worktrees/hubos-editor-20261019/public/hub-media/extract-audio-from-video/test-10s.mp4 mean_volume: -21.1 dB
out.mp3 mean_volume: -21.5 dB
out.wav mean_volume: -21.1 dB
c.mp3 mean_volume: -21.5 dB

## Two track 30 s clip (script db.sh)
vd() { ffmpeg -hide_banner "$@" -af volumedetect -f null - 2>&1 | grep mean_volume | sed "s/.*: //"; }
ffmpeg -v error -y -f lavfi -i testsrc2=size=640x360:rate=25:duration=30 -f lavfi -i "sine=frequency=330:sample_rate=44100:duration=30" -f lavfi -i "anoisesrc=amplitude=0.02:duration=30:sample_rate=44100" -f lavfi -i "sine=frequency=550:sample_rate=44100:duration=30" -filter_complex "[1:a][2:a]amix=inputs=2:normalize=0,pan=stereo|c0=c0|c1=c0[a1];[3:a]volume=0.5,pan=stereo|c0=c0|c1=c0[a2]" -map 0:v -map "[a1]" -map "[a2]" -c:v libx264 -preset veryfast -crf 30 -c:a aac -b:a 192k two.mp4
echo src-t1 $(vd -i two.mp4 -map 0:a:0)
echo src-t2 $(vd -i two.mp4 -map 0:a:1)
ffmpeg -v error -y -i two.mp4 -vn -c:a libmp3lame -b:a 128k two.mp3; echo mp3-default $(vd -i two.mp3)
ffmpeg -v error -y -i two.mp4 -vn -map 0:a:1 -c:a libmp3lame -b:a 128k two2.mp3; echo mp3-track2 $(vd -i two2.mp3)
--- output
src-t1 -21.0 dB
src-t2 -27.1 dB
mp3-default -21.5 dB
mp3-track2 -27.5 dB

161479 c.mp3
163011 out.aac
161270 out.mp3
1765454 out.wav