Release Notes for Safari Technology Preview 34

Safari Technology Preview Release 34 is now available for download for macOS Sierra and betas of macOS High Sierra. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. This release covers WebKit revisions 217978-218629.


  • Added WebRTC options to the Developer menu
  • Disabled Legacy WebRTC API in the Experimental Features menu by default (r218169)
  • Changed behavior to close NetworkProcess WebRTC sockets as soon as the Web Process no longer needs them (r218432)
  • Added support for receive-only SDP offers through addTransceiver (r218431)
  • Changed handling capture status based on MediaStreamTrack (r218399)
  • Changed RTCPeerConnection to return RTCSessionDescriptionInit instead of RTCSessionDescription (r218335)
  • Fixed a cloned MediaStreamTrack to not mute the other tracks using the same source (r218497)
  • Fixed RTCPeerConnection getReceivers() to return transceivers that have an active receiver but no active sender (r218182)
  • Fixed the screen going into sleep mode during WebRTC video (r218151)


  • Fixed high CPU usage when entering fullscreen or seeking during MSE video playback (r218463)
  • Fixed seeking during MSE video playback where audio would begin playing long before rendering the video (r218150)
  • Fixed video flashing black when switching back to a tab (r218291)
  • Improved media controls rendering for long-loading media files (r218600)
  • Prevented media elements continuing to load media data after navigation (r218016)


  • Made Object.assign faster by rewriting it in C++ (r218348)
  • Reduced Structure size (r218070)
  • Updated RegExp.prototype.[@@search]] implementation according to the latest specifications (r218051)
  • Fixed PreTypedArray constructor with a string to not throw an exception (r218082)


  • Applied img-src CSP directive to favicon loads (r218015, r218026)
  • Implemented W3C Secure Contexts Draft Specification (r218027, r218028, r218155, r218196)
  • Restricted filtered painting across cross-origin boundaries with transforms (r218300)
  • Added allow-popups-to-escape-sandbox attribute support for <iframe> elements (r218000)
  • Added Subresource Integrity as an experimental feature (r217996)

Web Inspector

  • Added grid to image previews to clarify transparency and image size (r218159)
  • Fixed console message icons that overlap the source location (r218243)
  • Fixed pretty print, type info, and code coverage buttons disappearing after switching tabs (r218305)
  • Fixed SVG files and favicon files that don’t display properly (r218298)
  • Fixed the search highlight not showing up in resources when paused (r218359)
  • Fixed showing non-shadow children of an element with a shadow root (e.g. <video>) (r218020)


  • Fixed the meter element not respecting the writing direction (r218468)
  • Fixed WebGPU contexts to have a back reference to the canvas element (r218624)
  • Fixed CSS transitions added while page is not visible so they start animating when the page becomes visible (r217997)
  • Fixed IndexedDB.getAll() use inside a Web Worker (r218041)


  • Moved SubtleCrypto from the experiemental features menu (r218129)
  • Removed unsupported AES_CMAC, DH, and CONCAT (r218030)


  • Fixed several miscellaneous bugs found from web platform tests (r218216)


  • Added an experimental feature setting for asynchronous frame scrolling (r218534)


  • Exposed the inline property as an accessibility attribute (r218226)

Bug Fixes

  • Fixed header rendering incorrectly when initially loaded (r218257)
  • Fixed scrubbing backward on a YouTube video