Hi, I also tried this approach and I can reproduce this behavior. When writing the metadata I am never able to read them back with the python interface.
This is a BaseTransform implementation to write metadata and a python script with a probe on the fakesink to read the written metadata.
I cannot read the metadata neither from the BaseTransform itself, just after writing them, nor from the probe in a downstream element.
add_custom_meta.py:
import gi
import random
gi.require_version('Gst', '1.0')
gi.require_version('GstBase', '1.0')
gi.require_version('GstVideo', '1.0')
from gi.repository import Gst, GObject, GstBase, GstVideo
import numpy as np
Gst.init(None)
FIXED_CAPS = Gst.Caps.from_string('video/x-raw,format=I420,width=[1,2147483647],height=[1,2147483647]')
class ExampleTransform(GstBase.BaseTransform):
__gstmetadata__ = ('Example','Transform', 'Example', 'example')
__gsttemplates__ = (Gst.PadTemplate.new("src", Gst.PadDirection.SRC, Gst.PadPresence.ALWAYS, FIXED_CAPS),
Gst.PadTemplate.new("sink", Gst.PadDirection.SINK, Gst.PadPresence.ALWAYS, FIXED_CAPS))
def do_transform_ip(self, buffer):
try:
# Step 1: write metadata
custom_meta = buffer.add_custom_meta("my_custom_meta")
meta_structure = custom_meta.get_structure()
value = random.randint(0, 1000)
meta_structure.set_value("value_name", value)
# Step 2: try to read the just written metadata
custom_meta2 = buffer.get_custom_meta("my_custom_meta")
meta_structure2 = custom_meta2.get_structure()
value2 = meta_structure2.get_value("value_name")
# Structure 2 has a different address, it is a copy. The read value is None
print(f"add_custom_meta: meta address {hash(custom_meta)}")
print(f"add_custom_meta: meta2 address {hash(custom_meta2)}")
print(f"add_custom_meta: meta struct address {hash(meta_structure)}")
print(f"add_custom_meta: meta2 struct address {hash(meta_structure2)}")
print(f"add_custom_meta: written value: {value} - read value {value2}")
return Gst.FlowReturn.OK
except Gst.MapError as e:
Gst.error("Mapping error: %s" % e)
return Gst.FlowReturn.ERROR
GObject.type_register(ExampleTransform)
__gstelementfactory__ = ("add_custom_meta", Gst.Rank.NONE, ExampleTransform)
custom_meta_bug_main.py:
import gi
gi.require_version("Gst", "1.0")
gi.require_version("GstApp", "1.0")
gi.require_version("GstVideo", "1.0")
from gi.repository import Gst, GstApp, GObject, GLib, GstVideo
Gst.init(None)
def transform_func(*args):
print("in transform")
return True
meta_info = Gst.meta_register_custom("my_custom_meta", ["tag"], transform_func, None)
def read_custom_meta_callback(pad, info):
buffer = info.get_buffer()
custom_meta = buffer.get_custom_meta("my_custom_meta")
meta_structure = custom_meta.get_structure()
value = meta_structure.get_value("value_name")
print("--")
print(f"probe callback: meta address {hash(custom_meta)}")
print(f"probe callback: meta struct address {hash(meta_structure)}")
print(f"probe callback: read value {value}")
print("=============================")
return Gst.PadProbeReturn.OK
def main():
pipeline = Gst.parse_launch("videotestsrc ! video/x-raw,format=I420,width=1920,height=1080,framerate=30/1 ! add_custom_meta ! fakesink name=meta_reader")
src_element = pipeline.get_by_name('meta_reader')
srcpad = src_element.get_static_pad('sink')
_ = srcpad.add_probe(Gst.PadProbeType.BUFFER, read_custom_meta_callback)
mainloop = GLib.MainLoop()
pipeline.set_state(Gst.State.PLAYING)
mainloop.run()
if __name__ == "__main__":
main()
And here is a sample of the output for an execution of the main script:
=============================
add_custom_meta: meta address 139861247934640
add_custom_meta: meta2 address 139861247934640
add_custom_meta: meta struct address 139861248072480
add_custom_meta: meta2 struct address 139861248072784
add_custom_meta: written value: 309 - read value None
--
probe callback: meta address 139861247934640
probe callback: meta struct address 139861248072480
probe callback: read value None
=============================
add_custom_meta: meta address 139861247934688
add_custom_meta: meta2 address 139861247934688
add_custom_meta: meta struct address 139861248072480
add_custom_meta: meta2 struct address 139861248072784
add_custom_meta: written value: 940 - read value None
--
probe callback: meta address 139861247934688
probe callback: meta struct address 139861248072480
probe callback: read value None
=============================
add_custom_meta: meta address 139861247934736
add_custom_meta: meta2 address 139861247934736
add_custom_meta: meta struct address 139861248072480
add_custom_meta: meta2 struct address 139861248072784
add_custom_meta: written value: 253 - read value None
--
probe callback: meta address 139861247934736
probe callback: meta struct address 139861248072480
probe callback: read value None
=============================