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A few ideas looking for feedback

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A few ideas looking for feedback
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Jan Schmidt 2003-04-28 22:09:38 +00:00
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# OpenGL usage
How to set up openGL using plugins in such a way that they can
render to an on-screen window, or offscreen equally?
eg:
superfoo3d ! glwindow
or
superfoo3d ! gloffscreen ! xvideowindow
This would imply that there is some mime type which connects a glwindow/gloffscreen and a GL using component sensibly. I don't see that there is any actual
data to send, however - the only purpose of the glwindow/gloffscreen is to
set up an openGL context and then 'output' it somehow one the superfoo3d has
finished drawing each frame.
In the case of glwindow, 'output' it means translate into an on-screen window,
but for gloffscreen it means produce a video packet and go.
These components really need some other 2 way communication, rather than the
pads metaphor, I think?

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# Compositing and video overlays.
We want a way to composite a video frame and an overlay frame. The video frame is as we expect, the overlay is a normal video frame + an alpha mask. In the following monologue, please consider that I mean RGB/I420/YV12/YUY2 wherever I say RGB.
So we have a plugin with 2 sinks and one src:
+----------------+
|video |
| video|
|overlay |
+----------------+
What should the format for the overlay data look like?
Ideas:
* RGBA - 4 byte per pixel video frame
* RGB+A - 3 Bytes per pixel video frame, then 1 byte per pixel overlay frame.
A new mime type, or a variation on video/raw? I'm not sure
* Overlay is actually 2 sinks, one takes a RGB/YUV data the other the alpha channel.
I'm not sure which approach is better, but I think it is probably neatest to
use RGB+A, and then have a separate plugin which has 2 sinks and converts an
RGB/YUV stream plus an alpha stream into an RGB+A stream. The benefit of RGB+A over RGBA in this scenario, is that it is easier (correct me if I'm wrong) to optimise 2 block copies which appends an alpha frame to a RGB frame than it is to
do the many copies required to interleave them into an RGBA stream.
So, I see this producing a few new plugins:
videooverlay - takes an RGB and an RGB+A frame from 2 sinks, does the overlay (according to some properties) and outputs a result frame in RGB or RGB+A (as negotiated) format on 1 src.
rgb2rgba - takes 1 RGB frame and one A frame from 2 sinks and outputs RGB+A on 1 src. If the A sink is not connected, we just add a fixed alpha channel based on an object-property.
rgb2rgba - takes an RGB+A frame and discards the RGB component.
textoverlay - This plugin, instead of taking a video frame and overlaying text, can just output an RGB+A stream with appropriate timestamping. This prevents duplicating code to composite with an alpha mask and allows us to optimise it in one spot only.