[gst-devel] Questions on image "muxing"

Nagy Gergely gergely.nagy at neteyes.hu
Sat Jan 1 11:42:03 CET 2005

> Op za 01-01-2005, om 19:04 schreef Nagy Gergely:
> > Basically, what I imagine is a generic overlay "muxer", that takes two
> > images and merges them. So far, I did not find anything like it, but it
> > might happen I'm just wasn't looking hard enough.
> You probably mean 'videobox' (I think that's how it's called), it's what
> Fluendo's streaming server uses to overlay images or text on video
> frames. It can also mux two video streams (and make use of alpha
> information - I'm not sure if it can crossfade but that's certainly not
> difficult to add if it doesn't. 

Mhm, so it's possible, good =)

What I had in mind, is something like a loop element, with two sinks and
a pad: onto the two sinks, I attach the background image, to the other,
the image to merge. So the whole thing operates on a per-frame basis.
This way, I can have a filter before any of the imgages that alters its
alpha channel or opacity property, or anything of that sort. That way, I
don't have to code all that into the muxer element.

(This is roughly how our current solution works)

Will have a look at flumotion, maybe we can use what they have there!
Thanks for the pointer!

> Textoverlay has a different purpose and
> therefore is not appropriate for you, I think. It's primary use is title
> screens, subtitles and such. We'll eventually want to support scrolling
> text as well, but it doesn't do that right now.

What my aim with the generic overlayer is, that one would be able to
specify the position of the merge (along with other properties), so
scrolling would be as easy as rendering the text once into a bin, then,
feed that to the scroll filter, which would simply proxy the thing along
as-is, and only changing its x and y properties, which the overlay
filter uses to determine where to merge the image.

This is light on resources (one doesn't have to re-render the text each
time, for example), and is much more flexible, than writing a
text-scroller - this way, one can scroll images too, for example.

PS: You don't have to Cc me, I'm on the list :)

Nagy Gergely <gergely.nagy at neteyes.hu>
NetEyes Kft.

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