YT Levelr

Automatic loudness levelling for YouTube — useful for podcasts

An extension that automatically equalizes the volume of YouTube videos, especially podcasts where every producer has their own idea of what the correct levels should be. Features - Automatic Loudness Normalization: Automatically adjusts audio levels between videos to create a consistent listening experience - Smart Gain Management: Uses asymmetric gain limits (more aggressive cuts than boosts) to prevent sudden loud blasts - Gradual Confidence Growth: Gain limits start narrow and widen linearly until full adjustment range is available at 30s, allowing the algorithm to make small initial corrections before committing to its final decision - Drift Correction: Slow automatic correction every 3 minutes after lock to handle long-term level shifts - Noise Floor Protection: Ignores silence periods to avoid skewing measurements - Local Processing Only: All audio processing happens entirely within your browser - no data is collected or transmitted How It Works YT Levelr uses the Web Audio API to intercept audio output from YouTube's video element and applies automatic gain correction: - Audio Interception: Creates a source node from YouTube's video element - RMS Measurement: Continuously measures Root Mean Square (RMS) amplitude of the audio - Gain Calculation: Compares measured level against your target level (default: -22 dBFS) - Smooth Transitions: Applies gain changes with asymmetric attack/release times to protect against sudden loud sounds - Locking: After 30 seconds, gain locks and only drift correction applies Strategy Details - Gradual Confidence Growth: - Starts with narrow gain limits (±6dB/+3dB) at t=0 for cautious initial corrections - Limits widen linearly over time as confidence in measurement grows - At 30s, full range is available (±20dB/+15dB) and gain locks to its final decision - Asymmetric Treatment: Cuts are permitted more aggressively than boosts because a sudden loud blast is worse than staying quiet for a few seconds - Gain Transitions: Faster transitions for cuts (0.15s) than boosts (1.2s) to protect against sudden loud audio Visual Indicators The popup displays real-time information: - Applied Gain: Current gain multiplier being applied - Status: Shows measuring, locked, or disabled state - Confidence Bar: Progress toward full confidence (100% at 30s) - Waveform Display: Visual representation of audio levels with target line