[Bug 663822] New: [subtitleoverlay] should not hardcode to use textoverlay element

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=663822
  GStreamer | gst-plugins-base | 0.10.x

           Summary: [subtitleoverlay] should not hardcode to use
                    textoverlay element
    Classification: Platform
           Product: GStreamer
           Version: 0.10.x
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: bcxa.sz at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


subtitleoverlay bin is hardcoded to use textoverlay element when playbin2
detect subtitle in multimedia file.

The textoverlay is assumed that the upstream video element will provide decoded
video buffer then blit the subtile buffer with the decoded video buffer.

This is not the case for embedded system. Some embedded system in order to use
hardware accelation, the decoded video data can be in kernel space and send to
display component from kernel to kernel. So in the user space, it can be the
fake buffer from upsream video decoder element then it is not needed to blit
the subtitle buffer. And the subtitle buffer can push to downstrean element
(sink element) to display.

So I think subtitleovelay bin is hard coded to use textoverlay is not flexible.

One of basic idea of gstreamer is to select component with same caps in the
sink pad according to RANK RPIORITY. But this is not the case for
subtitleoverlay bin now. We provide own textoverlay element with same sink pad
caps as gstreamer native textoverlay. But our own textoverlay element will not
selected even though it has higher RANK.

Sorry, I am not native english speaker. Please let me know if you don't
understand.

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