[Bug 794744] New: Data is none in buffer from GstVideo.VideoFrame

["GStreamer" (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794744

Bug ID: 794744
Summary: Data is none in buffer from GstVideo.VideoFrame
Classification: Platform
Product: GStreamer
Version: unspecified
OS: Linux
Status: NEW
Severity: normal
Priority: Normal
Component: gst-python
Assignee: gstreamer-***@lists.freedesktop.org
Reporter: ***@gmail.com
QA Contact: gstreamer-***@lists.freedesktop.org
GNOME version: ---

Hey,

When trying to get buffer data from GstVideo.VideoFrame when inheriting from
GstVideo.VideoFilter using do_transform_frame.

Steps to Reproduce:
Run code below and it will show none for buffer

Actual Results:
No data in buffer
Black screen from ximagesink(which may be because i have to push outframe back.
Dont know if i need to since i dont change any of the frame.)

Expected Results:
Gives a Gst.Buffer which should hold a full image frame to be manipulated (in
the docs here
https://lazka.github.io/pgi-docs/GstVideo-1.0/classes/VideoFrame.html it says
that a Gst.Buffer will be returned)

Build Date & Hardware:
March 26 2018 on ubuntu 16.04 LTS

Additional Builds and Platforms:
Havnt tested on any other builds

Additional Information:

I believe my Gstreamer version is
gst-launch-1.0 version 1.8.3
GStreamer 1.8.3
https://launchpad.net/distros/ubuntu/+source/gstreamer1.0

This was found by using gst-launch-1.0 --version in the command prompt



The buffer is None. Here is some sample code, let me know if i should post
anything else or if i can help. Thanks for your time.



import sys
import gi

gi.require_version('Gst', '1.0')
gi.require_version('GstVideo', '1.0')

from gi.repository import GObject, Gst, GstVideo

Gst.init(sys.argv)
GObject.threads_init()
Gst.segtrap_set_enabled(False)


class GstTimestamp(GstVideo.VideoFilter):
__gstmetadata__ = ('<longname>', '<classification>',
'<description>', '<author>')

__gsttemplates__ = (Gst.PadTemplate.new("sink",
Gst.PadDirection.SINK,
Gst.PadPresence.ALWAYS,
Gst.Caps.new_any()),
Gst.PadTemplate.new("src",
Gst.PadDirection.SRC,
Gst.PadPresence.ALWAYS,
Gst.Caps.new_any()))

def __init__(self):
GstVideo.VideoFilter.__init__(self)

def do_transform_frame(self,inframe,outframe):

#this should give me that data for the frame
data = inframe.buffer
#data is None
print data

#dont know if im properly sending data back since
#i just get blank screen
return Gst.FlowReturn.OK


#used for registration
def plugin_init(plugin):
Gst.Element.register(plugin, 'timestamper', 0,
GObject.type_register(GstTimestamp))
return True

def init():
version = Gst.version()
Gst.Plugin.register_static(
version[0], version[1], 'timestamper', 'Timestamper',
plugin_init, '1.0', 'GPL', 'timestamper',
'plugins-demo', 'demo')

init()


def connect(bus, name):
def _connect(f):
bus.connect(name, f)
return f
return _connect

def main():
pipeline = Gst.parse_launch('videotestsrc ! timestamper ! ximagesink')

bus = pipeline.get_bus()
bus.add_signal_watch()
#Gst.debug_set_active(True)
#Gst.debug_set_default_threshold(4)

@connect(bus, "message::error")
def on_error(bus, message):
pipeline.set_state(Gst.State.NULL)
exit(message.parse_error())

@connect(bus, "message::eos")
def on_eos(bus, message):
pipeline.set_state(Gst.State.NULL)
exit(0)

pipeline.set_state(Gst.State.PLAYING)
loop = GObject.MainLoop()
try:
loop.run()
except(KeyboardInterrupt):
pass

pipeline.set_state(Gst.State.NULL)

if __name__ == '__main__':
main()

["GStreamer" (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794744

Dineth W <***@gmail.com> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |***@gmail.com

["GStreamer" (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794744

Mathieu Duponchelle <***@gmail.com> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |***@gmail.com

--- Comment #1 from Mathieu Duponchelle <***@gmail.com> ---
Investigated, this is unfortunately a gobject-introspection bug:

pygobject obtains the value of the field with g_field_info_get_field(), which
in turn uses the offset returned by g_field_info_get_offset(), which is wrong
(differs from G_STRUCT_OFFSET (GstVideoFrame, buffer).

Digging a bit deeper, the VideoFrame is defined as:

struct _GstVideoFrame {
GstVideoInfo info;
GstVideoFrameFlags flags;

GstBuffer *buffer;
}

and GstVideoInfo ends with a union:

struct _GstVideoInfo {
...

union {
struct {
GstVideoMultiviewMode multiview_mode;
GstVideoMultiviewFlags multiview_flags;
GstVideoFieldOrder field_order;
} abi;
/*< private >*/
gpointer _gst_reserved[GST_PADDING];
} ABI;
}

The union isn't taken into account by the return of get_offset, this is easy to
determine as g_field_info_get_offset(buffer_field_info) == G_STRUCT_OFFSET
(GstVideoInfo, ABI).

The implementation of the get_offset function ends with:

blob = (FieldBlob *)&rinfo->typelib->data[rinfo->offset];

return blob->struct_offset;

I haven't investigated past this point, I would suggest reporting this issue to
the gobject-introspection devs, ideally with a smaller test case, though the
problem here is pretty clear cut.

["GStreamer" (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794744

--- Comment #2 from Mathieu Duponchelle <***@gmail.com> ---
correction: g_field_info_get_offset(flags_field_info) == G_STRUCT_OFFSET
(GstVideoInfo, ABI) obviously

["GStreamer" (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794744

GStreamer system administrator <***@gstreamer.net> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |OBSOLETE

--- Comment #3 from GStreamer system administrator <***@gstreamer.net> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
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