[Bug 702632] New: basetransform acceptcaps can be very very slow

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=702632
  GStreamer | gstreamer (core) | git

           Summary: basetransform acceptcaps can be very very slow
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: sjoerd at luon.net
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Created an attachment (id=247248)
 --> (https://bugzilla.gnome.org/attachment.cgi?id=247248)
Proposed patch

I've got a logitech C910 camera, which supports quite a few different
resolutions. Apparently this is a great way of trigger caps explosion corner
cases :)

On my system a simple test program which just creates a camerabin, using
wrappercamerabinsrc takes more then 50 seconds before it starts sreally
treaming frames:

$ GST_DEBUG='*v4l2src*:4' gst-uninstalled ./test 2>&1 | grep  gst_v4l2src_fill

0:00:23.129465038 10324       0xaae990 INFO                 v4l2src
gstv4l2src.c:861:gst_v4l2src_fill:<v4l> sync to 0:00:00.500000000 out ts
0:00:20.160806192
0:00:52.687093166 10324       0xaae990 INFO                 v4l2src
gstv4l2src.c:861:gst_v4l2src_fill:<v4l> sync to 0:00:01.000000000 out ts
0:00:50.355114373
0:00:52.691789600 10324       0xaae990 INFO                 v4l2src
gstv4l2src.c:861:gst_v4l2src_fill:<v4l> sync to 0:00:01.500000000 out ts
0:00:50.728432813

Almost all the time is taking up by intersections triggers by caps queries in
acceptcaps of basetransform.. With the attached patch the time before the
second frame starts is reduces to a bit more then 15 seconds:
0:00:14.980203785 13227      0x26ca990 INFO                 v4l2src
gstv4l2src.c:861:gst_v4l2src_fill:<v4l> sync to 0:00:00.500000000 out ts
0:00:12.103921631
0:00:15.980073337 13227      0x26ca990 INFO                 v4l2src
gstv4l2src.c:861:gst_v4l2src_fill:<v4l> sync to 0:00:01.000000000 out ts
0:00:13.104369148

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