[osg-users] Generating a Video

[Anders Backman]

I have implemented a class that does this multithreaded imagecapture and it
works fairly well.
It was adopted to osgProducer so I have to verify that it also works for
osgViewer.
It generates screens as images and pushes them to a worker that write bmp:s
to disk.

Then I use bmp2avi (under windows to generate avi:s, or the Bink/Smacker
toolset to generate them).


I will verify the code with latest osg and post it back....

/Anders


On 8/13/07, Robert Osfield <robert.osfield at gmail.com> wrote:
>
> I haven't put together a video from an OSG app yep, but its inevitable
> one day I'll need to so I thought I'd pen down what I think might be a
> nice way to tackle it.  This might also be a good example to have
> added to the OSG, so users are welcome to add one :-)
>
> My thought was to have a slave Camera that tracks the master camera,
> but with an FBO or Pbuffer set to PAL dimensions (or whatever target
> res you want for the video), this will record the frames at the
> correct size, and without any toolboxes etc interfering.
>
> Second up would be to attach a post draw callback to the slave Camera,
> and in this callback you'd do the osg::Image::readPixels to do this
> for you.  In theory one could set up a PixelBufferObject to help speed
> to read up.  Next up you have to save this image to disk, or just
> cache it.   Now writing to disk will be slow, so you don't want to do
> this in the rendering thread, rather spawn an OperationThread to do
> the writing to disk, with a custom ImageWriteOperation added to the
> OperationThread.  Due to the asynchronous nature of write one will
> need to use a circular buffer of osg::Image, one at the head being
> written to by the rendering thread, and the rest being used by
> ImageWriteOperations, when the image is written to disk one simply
> then put the Image back into the buffer ready to be reused.
>
> Then once you've stopped your recording of images, you wait till the
> last frame is written to disk (the OperationThread's queue is empty)
> then you span a tool to glue all these frames together as a video.
> Potentially you could use video library like ffmpeg to do this in a
> background thread.
>
> Other little changes one could make would be to cut the framerate of
> the app down to 25fps to match the needs of the video, or perhaps even
> let the app run at a multiple, say 50 or 75fps and then blend frames
> together, and only write out at 25fps.
>
> Robert.
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>



-- 


________________________________________________________________
Anders Backman               Email:    andersb at cs.umu.se
HPC2N/VRlab                  Phone:    +46 (0)90-786 9936
Umea university              Cellular: +46 (0)70-392 64 67
S-901 87 UMEA SWEDEN         Fax:      +46 90-786 6126
                               http://www.cs.umu.se/~andersb
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