This is direct from the Qt website news:
Support of Qt 5.9 LTS ends in May 2020. If you are still with Qt 5.9 LTS, update to the soon released Qt 5.15 LTS or Qt 5.12 LTS is recommended. If you can’t update, extended support is available for an additional fee after the standard support ends.
Version 5.9 is what MLT-Shotcut currently uses and which is needed for WebVfx. Later versions of Qt do not support Qt-Webkit upon which WebVfx depends.
If/when Dan updates MLT-Shotcut to a supported version of Qt it will not be possible to migrate WebVfx, so it will have to be abandoned. I could be wrong about this and if @shotcut were to correct me I would be more than happy.
I have been looking at a couple of workarounds for when (if?) this happens, the first of which is obvious:
Keep a copy of the most recent version of Shotcut that supports WebVfx to handle those existing projects that use the Text:HTML filter, since an upgrade of Qt will break them.
I have been experimenting with SHAREX (https://getsharex.com/) which does screen recording. Unfortunately it only runs on Windows systems, but there are other screen recorders that run on Linux and \MacOs.
I created a reasonably heavy CSS animation (a spinning translucent coloured cube with writing on each side). I then started the animation and used sharex to record the screen. It did a reasonable job recording at 30fps, but there was definitely some jerkiness where it struggled to keep up at that frame rate.
So what I did was I increased the duration of the animation by a factor of 3 (10 secs -> 30 secs) and I also reduced the framerate in Sharex by a factor of 3 from 30fps to 10fps. I then recorded the screen and input the resulting MP4 file into Shotcut and increased its speed by a factor of 3 and ended up with a much smoother 10 second clip than I did originally.
Recording a browser window is ugly, however Google Chrome, Microsoft Edge and Firefox have a feature whereby you can make the window full-screen (function key F11). No tabs or other browser “real estate” is visible. Sharex has the ability to record a full-screen.
While this technique cannot be used to replace those WebVfx Text:HTML filters that process data stored in the video being edited in shotcut (such as the “sniper-scope” and “persistence” filters and the “gl-transitions”, it is quite a good compromise for Text:HTML filters that are independent of the video data, such as video credits, titles, text-manipulation (e.g. exploding text, typewriter-text, text-flow etc). In fact, in some ways it is better since you can now use all of the modern CSS3 animation techniques (including perspective and 3D) that are not supported by WebVfx, Text:HTML or Text:Simple.
Does anyone have any other suggestions?