GStreamer zero copy read only buffer duplication

[Ádám Balázs]

Hi,

I have a GStreamer pipeline with an appsink:

filesrc location=test.mp4 ! decodebin ! video/x-raw ! queue
max-size-bytes=0 max-size-time=100000000 ! appsink name=appSink
sync=false max-buffers=1 drop=false

I pull a sample from the appsink then I get the buffer, map it read-only
and store the map info (to access raw memory later):

sample: Gst.Sample = self.__sink.pull_sample()
self.__buffer: Gst.Buffer = sample.get_buffer()
self.__buffer_map: Gst.MapInfo = self.__buffer.map(Gst.MapFlags.READ)

Then I would like to use the same data (without copying it) in an output
pipeline for e.g.:

appsrc name=appSrc block=true !
video/x-raw,format=(string)NV12,width=1920,height=1080,framerate=30/1
! videoconvert ! ximagesink

To do this it is the best I could come up with:

shared_buffer_memory = self.__buffer.get_all_memory()
buf = Gst.Buffer.new()
buf.insert_memory(-1, shared_buffer_memory)
self.__src.push_buffer(buf)#sleep(0.05)

If I do this I see the first frame correctly but all the other frames are
green. It is fine, because the underlying memory of buf goes out of scope
and freed meanwhile. If I put sleep(0.05) after push_buffer it displays all
of the frames, but I think the memory behind the buffer is double-freed:

** (python3.9:6745): CRITICAL **: 09:23:54.645: gst_vaapi_image_unmap:
assertion 'image != NULL' failed

I would like to get the frames from the appsink then push them into output
pipelines without copy. What would be the best approach to do this? (a
single pipeline is not suitable in my case)

Kind regards,
Adam
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