TEMPO Slider Autor: XTAL

TEMPO Slider gives DJs and crate diggers DAW-grade pitch-preserving tempo control across multiple music stores. Hear track previews at your target BPM without the chipmunk effect — just like a real CDJ.

WHY THIS EXTENSION
Other tempo extensions are usually single-site, and most just change playbackRate (which shifts the pitch with the tempo). TEMPO Slider works on multiple stores and uses the same DAW-grade pitch-shifting engine (Rubber Band Library, compiled to WebAssembly) that professional audio software relies on — so you can change tempo while keeping the original key.

KEY FEATURES
• MASTER TEMPO (pitch keep) — DAW-grade Rubber Band Library via WebAssembly. Change tempo while keeping the original key/pitch.
• Multi-site: YouTube, Bandcamp, Discogs, Beatport, Traxsource — plus any site you add via the popup.
• CDJ-style vertical TEMPO fader with ±6 / ±10 / ±16 / WIDE range.
• BPM display: manual TAP, audio-based AUTO detection, and DOM extraction on Beatport / Traxsource.
• Keyboard shortcuts (, / . for fine adjust, Shift for coarse, R reset, M master, T tap) and mouse wheel on the fader.
• Draggable panel with position memory.
• Multiple <audio> elements on a page are all controlled simultaneously (record-store-style preview lists).
• On Discogs, the panel controls the embedded YouTube preview directly — DAW-grade pitch keep applied to YouTube playback.

SUPPORTED SITES (BUILT-IN)
• YouTube (www.youtube.com — direct watch pages)
• Bandcamp (bandcamp.com)
• Discogs (discogs.com — YouTube previews on release pages)
• Beatport (beatport.com)
• Traxsource (traxsource.com)

ADDING YOUR OWN SITES
Click the extension icon on any other music site to add it. The extension will request permission, then enable the tempo control panel.

USE CASES
• Preview tracks at your target mixing BPM across stores before purchasing
• Practice mixing along to YouTube DJ sets at your own tempo
• Slow down or speed up while keeping the original key — for transcription, vocal practice, or DJ prep
• Tap to set source BPM and see live "current BPM" feedback as you move the fader

PRIVACY
This extension does NOT collect, track, or transmit any data. All processing happens locally in your browser. Source code is open at https://github.com/XTAL-JP/tempo-slider under GPL-2.0.

Note: this extension uses declarativeNetRequest to add CORS headers and remove Content-Security-Policy headers on supported sites. This is required for the audio processing pipeline (Rubber Band WASM library) to function inside the page's audio context. No data is sent externally.