HTML5 Syncer

About

Allows synchronisation of 2 HTML5 video and audio streams even on different tabs. Just click the popup to scan each page and press the "Sync" button to generate sync buttons next to the video/audio, then click them (preferably when both are paused at the right times) to synchronise. Press the "Flush" button to remove synchronisation.

The streams will pause, play, change playback rate and seek together.

You can check the Developer tools console for information.

N.B. You may have to go to "chrome://extensions/" and click the reload icon for this extension if the delay does not show up on the green sync button.

Changes:
15/01/2023 - More efficient code used when finding streams.
05/01/2023 - Faster code used when finding streams.
26/10/2022 - Improved element handling (e.g. searching for tags).
15/06/2021 - Handles streams waiting for data better.
18/05/2021 - Fixed issue where the delay could be written on the wrong button; made the buttons appear below audio tags if there is space at the bottom of the page.
16/05/2021 - Removed global variables from background script; improved message passing to tabs. 
04/05/2021 - Added "return true;" to the end of the "onMessage" functions.
19/04/2021 - Replaced 'chrome.extension.sendMessage/onMessage'
17/03/2021 - Minor code cleanup.
08/03/2021 - Updated manifest to v3.
24/02/2021 - Bugfix for last update.
24/02/2021 - Fixed issue where the sync button would appear closer to the top-centre than the top-left on some videos.
10/02/2021 - Better handling of 'Flush' event.
27/01/2021 - Minor amendments.
26/01/2021 - Now when the bar auto-hides, if you place the cursor where it was, it will reappear if it was clickable. Clicking the sync button whilst green now has no effect. Minor change to colour scheme, plus other fixes.
10/01/2021 - Fixed colour scheme of 'Scan' and 'Flush' buttons in popup (especially in dark mode).
13/12/2020 - Fixed issue that caused pause/play loop when seeking. Now can press 'Scan' more than once to generate sync buttons.
23/09/2020 - Keeps up to date with the tabs containing the synced videos.
Delay now displays immediately after syncing.
Event listeners now removed after the 'flush' action.
'src' is now correctly found for synced videos.
HTML button initialisation fixed.
20/09/2020 - Slight amendments to syncing procedure.
06/09/2020 - Improved console logging.
23/05/2020 - Fixed issues causing the wrong media element to be synced to, preventing the sync button being updated properly, and prevents the video automatically playing when the sync button is pressed sometimes.
07/05/2020 - Improved visibility CSS.
05/05/2020 - Adjusted visibility, changed event listeners and delay displayed in sync button.
04/03/2020 - Added close buttons, to remove sync buttons.
05/03/2020 - Placed sync and close buttons in a transparent div.