View source for QtWebEngine/VideoAcceleration

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

== Introduction ==

One of the most complex operations performed in internet browsers are video decoding and encoding. These compute operations can be executed as part of software implementation which runs on CPU, or the can be hardware accelerated and executed by dedicated hardware chips. By using hardware acceleration, the CPU can be offloaded and it is able to run meanwhile other execution tasks. This results in better interaction performance and it is crucial for embedded devices, where CPU processing power is limited. Moreover, using optimized dedicated hardware usually results in better video performance, quality and lower power consumption compared to software one.

=== TODO

- Needs to be supported by GPU hardware and drivers, usually only supporting some encoding
- Link to Chromium docs on video acceleration

== Chromium video acceleration platform support ==

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

* macOs: Video Toolbox
* ChromeOS on x86_64: VA-API
* ChromeOS on arm/tegra: V4l2
* Android: platform MediaCodec 
* Windows: DirectX Video Acceleration (DXVA)

On Linux, Chromium Project is mostly focused on 'desktop builds' which have enough processing power for video encoding and decoding using software based mulithreaded ffmpeg. Therefore, to avoid dealing with possible large number of hardware related bugs, acceleration support on chrome is by default disabled.

* https://bugs.chromium.org/p/chromium/issues/detail?id=463440
* https://bugs.chromium.org/p/chromium/issues/detail?id=137247

However, there is on going community effort to enable video acceleration using VA-API and some Linux distorts like 'Arch' patch chromium downstream already :

* https://codereview.chromium.org/1743543004
* https://codereview.chromium.org/1872393002
* https://chromium-review.googlesource.com/c/chromium/src/+/532294

== Chromium ==
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.

== Qt WebEngine ==
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:
* Enabling VA API in Qt 5.10 (?) for Chromium 61
* Implementing a punch hole in scenegraph
* Supporting GStreamer