Playing Speed Adjuster (PSA)

PSA is a bookmarklet that opens a small floating panel for the HTML5 <audio> and <video> on the current page. It works on any site; nothing in it is specific to one site.

• Speed from 0.25× to 4×: −/+ in 0.05 steps, presets (1, 1.25, 1.5, 1.75, 2, 2.5, 3), click the readout and type a value (1.6, 1.6x, 160%), or use the keyboard shortcuts.
• Applies the speed to every audio and video element on the page, including ones added later, ones inside open shadow roots and same-origin iframes, and off-page new Audio() players.
• Remembers the speed (and panel position) per site in localStorage. On a YouTube video, Just this channel (under the presets, or in the pill's speed menu) keeps a speed for that channel only, such as 1× for music, while other channels keep the site's. It also remembers where you left off in long recordings: play one again from the start and the panel offers Resume at 12:34.
• Keeps re-applying the speed so sites that reset playbackRate don't win.
• Play/Pause, −10 s / +20 s skips, a best-effort title and the real time left at your speed for the active item (the one that most recently started playing), plus a picture-in-picture button for videos. Use ‹ › to pick another item; the one you pick is outlined on the page, and scrolled into view if needed.
• Live streams (live radio, anything without an end) stay at normal speed, since speeding them up only causes buffering.
• Drag the panel by its top bar, or minimize it (or double-click the bar) to a small pill, remembered per site. The pill is just a blue dot and the speed until you point at it (or tab to it, or open its menu); then it shows PSA, − and + for 0.1 steps, a menu of common speeds behind the speed (which also drags the pill when pressed and moved), and the dot glows briefly when the pill appears or the speed changes, so it's easy to spot. In fullscreen it has a spot of its own: the top-left corner until you drag it during fullscreen, then wherever you left it (per site). There PSA fades away after 3 s without mouse movement, coming back when you move the mouse or the speed changes. While the mouse is over an embedded player, where PSA can't see it move, it doesn't fade. It stays open until you click × or run the bookmarklet again, and stays on top of fullscreen video and the page's own dialogs and popovers.

Install

Open the install page and drag the PSA button onto your bookmarks bar. The page also has demo tracks to try it on.

Or copy and paste: open dist/bookmarklet.txt on GitHub and click Copy raw file. Create a bookmark named PSA and paste the copied line as its URL. In Safari, bookmark any page, then use Edit Address… on it.

The test page has many kinds of players and a button that runs automated checks.

Click the bookmark on a page with audio or video to open the panel. Click it again, or click ×, to close it.

In Firefox, you can add the extension instead; see Firefox extension.

Firefox extension

In Firefox, add PSA from Firefox Add-ons to have it run on its own. It applies your speed and saves your place on every page, shows a small speed pill when something starts playing with sound (muted autoplay, such as ads, doesn't count), and opens the full panel from its toolbar button (or Alt+Shift+P). Players embedded from other sites, such as a YouTube video in a blog, follow the page's speed; when the page has no player of its own, the panel names the embedded one's site. Its settings page has a speed for sites without one of their own, switches for the pill and the keyboard shortcuts, a list of sites to leave alone, and the sites with a saved speed or places, and under each the YouTube channels with a speed of their own, each of which can be forgotten on its own. On its first visit to a site, it brings over the speed and places the bookmarklet saved there, then removes them from the site's storage. In private windows it uses your saved speeds but saves nothing. It updates itself, and needs Firefox 140 or later (142 on Android).

Keyboard shortcuts

While the panel is open, including minimized:

Key	Action
[	Slow down by 0.1
]	Speed up by 0.1
\	Set 1.5×, or back to 1× if already at 1.5×

They're ignored while you type in a text field, and ⌘ or Ctrl combinations are left to the browser (⌘[ is still Back). When PSA handles a key, the page doesn't also receive it.

Updating

Bookmarklets don't update themselves. The panel shows its version next to "PSA", and the install page shows the latest one. If yours is older, drag the button from the install page to your bookmarks bar again and delete the old bookmark. See Releases for what changed.

How it works

src/psa.js is the readable source and src/install.html is the install page template; npm run build rebuilds dist/ and the site's index.html. The build minifies the code with terser, checks the result parses, and writes strings in single quotes, and percent-encodes only the characters a javascript: URL can't carry, which keeps the bookmarklet around 35 KB.

• Finding media. Every 500 ms the panel queries each known document and shadow root for audio, video. It re-walks the page to find new open shadow roots and same-origin iframes every 2 s while the full panel is open, and every 6 s while it is minimized. In a background tab with nothing playing it rests until the tab is shown or something plays. The page's own dialogs and popovers report opening; a full look for them comes every 2 s. While the panel is open, HTMLMediaElement.prototype.play is wrapped so players that are never inserted into the page are found too; closing the panel restores it.

• Holding the speed. Live streams are left alone: a MediaStream source, an Infinity duration, or a duration that keeps growing (chunked live players such as RTHK live radio). One that was sped up before it was known to be live is put back to 1×. For everything else it sets both playbackRate and defaultPlaybackRate, the latter because load() resets to it. It re-applies whenever the page changes a player's speed or source, when a player starts, and on every tick. If a site resets an element more than 8 times in 2 s, the panel replaces that element's playbackRate setter so the page's writes are ignored ("speed locked" in the panel). Closing the panel removes the lock.

• Channel speeds. On YouTube, the channel is read from the video page's owner link (/@handle or /channel/…), but only once the page shows the video in the address and no ad is playing: moving to another video, YouTube keeps showing the old channel until the ad before it ends. Until then the site's speed applies. Channels with a speed of their own are saved with the site's values, up to 200; the one changed longest ago goes first.

• Resume positions. While the panel is open, it saves how far each recording longer than 3 minutes has got: every 5 s while playing, and at once on pause or when you leave the page. Recordings are told apart by the page they started playing on and their length (within 2 s, since players refine it as they load), because many sites play through a temporary blob: address that changes on every visit. The page address ignores tracking and start-time parameters such as utm_…, fbclid and t, and a player in an about:blank or srcdoc frame counts as part of the page around it. Positions in the first 30 s aren't saved, so starting over doesn't lose the old one, and a recording played to within 30 s of its end is forgotten. A stream that turns out to be live has its entry removed. They live in the site's localStorage under their own key, up to 100 per site.

Limits

• Media inside cross-site iframes (e.g. a YouTube embed on a blog) can't be reached by the bookmarklet. Open the embed's own page and run the bookmarklet there. The Firefox extension reaches them, but only to apply the speed.
• Closed shadow roots and players that use only the Web Audio API have no reachable media element.
• In browsers without the Popover API, the panel can't show over a bare fullscreen <video> or the page's own dialogs. In Chrome it shows over a bare fullscreen <video> or embedded player but can't be clicked there, since it can't go inside them; the keyboard shortcuts still work.

Development

Bump VERSION at the top of src/psa.js for each release; the build copies it to the install page.

npm ci
npm run build
npm test

npm ci installs the development tools (Node 20+): terser for the build and Playwright for the tests. Neither goes into the bookmarklet.

npm test opens the test page in headless Chrome, using your installed copy so nothing extra is downloaded. It runs the page's checks, checks that the mouse reaches PSA in real fullscreen, and clicks the real bookmarklet link on the install page. The test page covers labelled and unlabelled players, a shared heading with per-player labels, a stubborn page that keeps resetting the speed, a late-inserted player, shadow DOM, a same-origin iframe, off-page audio with Media Session, a playlist that calls load(), screen-reader-only text, a fullscreen container, live streams, a text field inside a closed shadow root, modal dialogs (one on top of another too), a popover over the whole page and a long recording; it also checks the skip buttons, the time left, picture-in-picture, resuming, the speed box, minimizing, the outline and the keyboard shortcuts. The runner also checks that the test server serves only the site's files.

To try a local build of the Firefox extension, open about:debugging#/runtime/this-firefox, click Load Temporary Add-on…, and choose dist/firefox/manifest.json. Firefox removes it when it restarts.

To try things by hand, run npm run serve, open http://127.0.0.1:8765/test/test-page.html, click Load PSA, pick a speed other than 1×, and click Run checks.

On every push, two GitHub Actions run:

• Build check: rebuilds and fails if the committed dist/ or index.html doesn't match src/.
• Tests: runs the same checks in Chromium, Firefox and WebKit (Safari's engine). It also checks the Firefox extension with Mozilla's add-on checker and a smoke test in Firefox (test/firefox-extension.mjs, which needs selenium-webdriver and geckodriver, so it runs only there).

Publishing a GitHub release runs a third, Firefox Add-ons, which submits that version of the extension to Firefox Add-ons with its source code, the notes for Mozilla's reviewers (src/firefox/reviewer-notes.txt) and the release's "What's new". It needs two repository secrets, AMO_JWT_ISSUER and AMO_JWT_SECRET, from an API key on Firefox Add-ons. A failed submission can be retried from the Actions tab with Run workflow and the release's tag.

License

MIT