[Bug 727124] New: ssim: reenable by implementing a basemixer class.

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=727124
  GStreamer | gst-plugins-bad | git

           Summary: ssim: reenable by implementing a basemixer class.
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: mathieu.duponchelle at epitech.eu
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


For our purposes of quality assurance in GES, we want to have a working video
stream comparator, in order to spot regressions and to ensure frame-accurate
editing.

SSIM fits the bill, but it is very difficult to port in a standard way.

My approach for fixing it has thus been to extract a base class from
videomixer, and only keep the relevant video measuring code in
videomeasure_ssim.c itself. 

It works well, and thanks to the colorspace conversions capabilities in
basemixer its usage is now much more straightforward. Additionnally, it will be
relatively easy to make ssim compare n-streams in one pass instead of just two
for now, and that will also be very useful performance-wise for us.

Example usage is :

gst-launch-1.0 -m videotestsrc num-buffers=30 ! ssim name=m ! videoconvert !
xvimagesink sync=false videotestsrc num-buffers=30 ! m.

As a bonus it shows that usage of the smpte pattern in videotestsrc is not
deterministic (Might not be very relevant though :)

I have also ported videomixer to that base class and have been using it since
multiple days, with no behaviour difference.

In the future, I think having that base class would be useful, for example when
comes the time of implementing a glmixer, but that's not critical.

Patches follow.

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