[gst-devel] video overlay plugin

Ronald Bultje rbultje at mail.bitfreak.net
Mon Apr 21 08:01:24 CEST 2003

Hey Gustavo,

On Mon, 2003-04-21 at 16:13, Gustavo J A M Carneiro wrote:
>   My idea is for this to be used to display subtitles in gst-player. 
> Any volunteers for that?  Should be fairly simple to do the rest.  We
> only have to insert textoverlay in the pipeline, read a subtitles file,
> and then change the 'text' attribute of the textoverlay from time to
> time.

The 'pipeline' idea is that this happens within the gstreamer pipeline
as well. mpegdemux, for example, can separate the subtitle streams.
There's another plugin (mpeg2subt) that decodes it into timestamped text
buffers, and the text plugin should read this and blit it onto the video
buffer. It can use the timestamp on the buffer for timing etc.
Properties and so on is nice, but it's basically a quick hack that
requires a lot of information from the application, while the idea of
gst is to keep apps simple and have plugins do all the work... The
pipeline then looks like:

filesrc->mpegdemux.video_00->   mpeg2dec-> textoverlay->xvideosink
                \\\                                     ///
                 \\\  .subtitle_00->mpeg2subt->///

See? In case of a separate subtitle file, you would open that using a
separate filesrc:

filesrc->subtitleparse->                     \\\
filesrc->mpegdemux.video_00->mpeg2dec-> textoverlay->xvideosink

This is the design proposed some time ago. You still need the
textoverlay plugin you've designed, don't worry about that, but you
transfer the text over a GstPad (timestamped) rather than over a

(Oh, we mostly use bugzilla (http://bugzilla.gnome.org/) for these kind
of things. If you prefer that, please upload the plugin there, it's easy
to lose track of stuff on the mailinglist, while that cannot happen
easily on bugzilla).

Anyway, thanks for the work!


Ronald Bultje <rbultje at ronald.bitfreak.net>
Linux Video/Multimedia developer

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