If anyone try out Sean's suggestion and get it to work, it would be great it they share an example so we don't all have to reinvent the wheel :)
Harald 2016-04-18 15:28 GMT+02:00 Andy <[email protected]>: > On Mon, Apr 18, 2016 at 9:05 AM, Sean Harmer <[email protected]> wrote: > >> 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 >> > > Thanks Sean. I wouldn't have thought to go through Qt Quick since I've > never used it and it's not on my radar. > > >> >> * 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. >> > > nvenc looks like it would be a big win for those with NVIDIA cards, and I > see AMD has the analogous VCE. > > > Thanks everyone for helping me get a better sense of the problem I'm > trying to solve! > > >> >> 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 >> > > --- > Andy Maloney // https://asmaloney.com > twitter ~ @asmaloney <https://twitter.com/asmaloney> >
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