Hi, I think it's possible, although it's not an out of the box feature yet, as Harald pointed out.
Have a look into this kind of approach: * Implement something similar to the Scene3DItem that allows to embed Qt 3D into a Qt Quick 2 scene * This requires using a little bit of private (for now) API to feed the Qt 3D renderer your own OpenGL context and to ask it to render when needed. * Use an FBO (as the Scene3D item does) as the render target - take care to tell the framegraph the size of this "external" render target. * Then, once the scene is rendered on your custom context, either: a) use glReadPixels to grab the contents of the texture you attached to the FBO and pass it to a software encoder. or b) use the texture id to pass the data to a hardware encoder such as nvenc without needing a round trip from the GPU->CPU->GPU. I think that can be made to work. Cheers, Sean On Monday 18 April 2016 08:38:21 Andy wrote: > On Mon, Apr 18, 2016 at 3:26 AM, Harald Vistnes <[email protected]> > > wrote: > > Hi Andy, > > > > An alternative is to use the FFMPEG encoding library instead of the > > command line tools. Then you can pass each frame to the video encoder as > > you generate it without writing them all to disk first. > > This is non-GPL software, so I can't use the lib directly (I should have > mentioned that). I haven't found a BSD or MIT lib that encodes the common > formats - is anyone aware of one? > > > The natural way to generate the QImages would be to render to an offscreen > > surface of the desired resolution, and then pass each frame to the video > > encoder. > > Great - so I'm on the right track! > > > Unfortunately, reading back the content of offscreen surfaces is missing > > in Qt3D. According to these it will not come before 5.8. > > > > https://bugreports.qt.io/browse/QTBUG-52136 > > https://bugreports.qt.io/browse/QTBUG-52074 > > > > So AFAIK we just have to wait with generating images and videos with Qt3D. > > Thanks Harald. Your report is exactly what I'm looking for... That's > unfortunate though - a real showstopper. > > > Cheers, > > Harald > > > > 2016-04-18 5:46 GMT+02:00 Andy <[email protected]>: > >> Goal: generate video with a user-specified resolution, frame rate, & > >> container/codec format from an animation in my Qt3D window > >> > >> (Disclaimer: I've never worked with video files before!) > >> > >> As far as I can tell, Qt doesn't provide a way to generate video files > >> directly, so I think I have to write a series of QImages to disk and use > >> them to generate a video using ffmpeg. This seems like it will take a > >> large amount of disk space, be pretty heavy on the I/O, and generally be > >> slow. Are there better solutions? > >> > >> If I need to do it that way though, I must generate QImages from my > >> existing Qt3DCore::QAspectEngine in my QWindow-derived class. I don't > >> see > >> a clear/elegant way to do this. > >> > >> I think I need to create an offscreen surface? window? with the correct > >> resolution and then somehow render & animate my scene to it, saving > >> snapshots as I move the camera. (I am already using QAbstractAnimation > >> to > >> move the camera, so I would use it to grab the snapshots as well.) Can I > >> use the same root entity in multiple QAspectEngines? (i.e. > >> setRootEntity() > >> to my root entity in the new offscreen and tell it to render.) > >> > >> Has anyone done this before? Is this even close to the right approach? > >> > >> (I'm using straight C++ - no QML.) > >> > >> Thanks! > >> > >> --- > >> Andy Maloney // https://asmaloney.com > >> twitter ~ @asmaloney <https://twitter.com/asmaloney> > >> > >> > >> _______________________________________________ > >> Interest mailing list > >> [email protected] > >> http://lists.qt-project.org/mailman/listinfo/interest > > --- > Andy Maloney // https://asmaloney.com > twitter ~ @asmaloney <https://twitter.com/asmaloney> -- Dr Sean Harmer | [email protected] | Managing Director UK KDAB (UK) Ltd, a KDAB Group company Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090 Mobile: +44 (0)7545 140604 KDAB - Qt Experts _______________________________________________ Interest mailing list [email protected] http://lists.qt-project.org/mailman/listinfo/interest
