[gst-devel] Drawing on a video stream

Mark Heslep mark at mitre.org
Tue Dec 5 22:12:30 CET 2006

Jerome Alet wrote:
> On Tue, Dec 05, 2006 at 02:53:07PM -0500, Mark Heslep wrote:
>> The question of overlaying graphics on a video stream (with gtk or other 
>> kit) was raised on the list before.  I have in mind something simple at 
>> first like a rectangle. The prior answer I believe was it could not be 
>> done once the stream was sinked onto a window, and that instead the 
>> drawing would have to be done directly on the data buffer itself w/ a 
>> custom element or handoff.
>> The problem with this is that all the drawing methods must be on a 
>> gdk.Drawable, i.e., a pixmap which resides in X11 space.  Is there in 
>> fact some way to use gtk drawing methods, or must one implement their 
>> own drawing routines?  Im aware of the Cairo text overlay element, I 
>> suppose I'll have at that for illustration.
> You could use a transparent PNG image used as an overlay 
Wouldn't that require X to support the transparency with compositing, 
etc? Without that any X window upon which the PNG is displayed is going 
to block what's underneath?
> and cause 
> the filesrc to reload it from time to time, and then have your 
> drawing tool save to a PNG file on disk (as frequently as needed). I 
> don't know how to cause the filesrc to reload a new file for each 
> frame though... 
> hth
> Jerome Alet

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