QtWebEngine/VideoAcceleration

Qt WebEngine does not currently support hardware accelerated decoding of videos.

Introduction

- What is video acceleration and do you really need it? Could you use a proprietary solution?

- To off-load CPU, especially important for embedded devices

- Needs to be supported by GPU hardware and drivers, usually only supporting some encoding

- Link to Chromium docs on video acceleration

Official Chromium enables video acceleration for Windows, macOS, and ChromeOS builds.

Regular Linux builds do not have video acceleration enabled, unless patched downstream by Linux distributions.

Current status of video decode acceleration for Qt WebEngine 5.9 and 5.10 is as follows:

Windows video acceleration does not work, see reasoning in https://codereview.qt-project.org/#/c/202314/ . Bottom line, this has not worked in any Qt WebEngine release due to ANGLE not working with multiple threads.
macOS video acceleration does "not" currently work, see reasoning in https://bugreports.qt.io/browse/QTBUG-60002 and attached patch. This used to work in versions <= Qt 5.8 (needs confirmation).
Linux (including embedded) video acceleration does ""not"" currently work. Work-in-progress VA-API support patch can be found at https://codereview.qt-project.org/#/c/209204/

Being considered: