webrtcbin create-answer returns unknown SDP type

Alexei Golovko alexej.golovko at gmail.com
Wed Jul 6 17:00:57 UTC 2022 

Great thanks for the workaround!

Should I report this as a bug on
https://gitlab.freedesktop.org/groups/gstreamer/-/issues with gst-python as
a project?

ср, 6 июл. 2022 г. в 14:40, Matthew Waters <ystreet00 at gmail.com>:

> Interesting.
>
> If you separate out this line:
>
> answer = promise.get_reply().get_value("answer")
>
> to:
>
> reply = promise.get_reply()
> answer = reply.get_value("answer")
>
> Then it will work.
>
> I think this has to do with the temporary copy that python makes when
> calling get_reply() that disappears too early?  This is likely a bug
> somewhere in the python bindings.
>
> This is the good case:
>
> 0:00:26.515777326 221861 0x555555684f00 ERROR              webrtcbin
> gstwebrtcbin.c:4584:_create_sdp_task: returning application/x-gst-promise,
> answer=(GstWebRTCSessionDescription)NULL;
> INFO     __main__:on answer: <Gst.Promise object at 0x7fffe8c593c0
> (GstPromise at 0x555555ade1b0)> <__gi__.GstWebRTCBin object at
> 0x7fffe9a43400 (GstWebRTCBin at 0x555555ac4120)> None
>
> Thread 3 "wrb:pc" hit Breakpoint 1, gst_webrtc_session_description_copy
> (src=0x7fffd81147b0) at
> ../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/rtcsessiondescription.c:72
> 72      if (!src)
> (gdb)
> Continuing.
> 0:00:31.294220789 221861 0x555555684f00 WARN               structure
> gststructure.c:2093:priv_gst_structure_append_to_gstring: No value
> transform to serialize field 'answer' of type 'GstWebRTCSessionDescription'
> INFO     __main__:reply: application/x-gst-promise,
> answer=(GstWebRTCSessionDescription)NULL;
> INFO     __main__:answer: <GstWebRTC.WebRTCSessionDescription object at
> 0x7fffe8c5a9e0 (GstWebRTCSessionDescription at 0x7fffd8116b20)>
> INFO     __main__:answer fields: <enum GST_WEBRTC_SDP_TYPE_ANSWER of type
> GstWebRTC.WebRTCSDPType>
> INFO     __main__:answer fields: <enum GST_WEBRTC_SDP_TYPE_ANSWER of type
> GstWebRTC.WebRTCSDPType> 3
> INFO     __main__:answer fields: <enum GST_WEBRTC_SDP_TYPE_ANSWER of type
> GstWebRTC.WebRTCSDPType> answer
> INFO     __main__:answer sdp is None: False
> INFO     __main__:answer fields: <GstSdp.SDPMessage object at
> 0x7fffe8c5aa40 (GstSDPMessage at 0x7fffd811a740)>
> INFO     __main__:answer sdp: v=0
>
> Bad case:
>
> 0:00:36.984435665 222001 0x555555685300 ERROR              webrtcbin
> gstwebrtcbin.c:4584:_create_sdp_task: returning application/x-gst-promise,
> answer=(GstWebRTCSessionDescription)NULL;
> INFO     __main__:on answer: <Gst.Promise object at 0x7fffe8c593c0
> (GstPromise at 0x555555aca2c0)> <__gi__.GstWebRTCBin object at
> 0x7fffe8c199c0 (GstWebRTCBin at 0x555555ac4120)> None
>
> Thread 3 "wrb:pc" hit Breakpoint 1, gst_webrtc_session_description_copy
> (src=0x7fffd8116150) at
> ../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/rtcsessiondescription.c:72
> 72      if (!src)
> (gdb)
> Continuing.
>
> Thread 3 "wrb:pc" hit Breakpoint 2, gst_webrtc_session_description_free
> (desc=0x7fffd8116760) at
> ../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/rtcsessiondescription.c:92
> 92      g_return_if_fail (desc != NULL);
> (gdb) bt
> #0  gst_webrtc_session_description_free (desc=0x7fffd8116760) at
> ../subprojects/gst-plugins-bad/gst-libs/gst/webrtc/rtcsessiondescription.c:92
> #1  0x00007fffe9e30008 in g_value_unset (value=value at entry=0x7fffd8118330)
> at ../subprojects/glib/gobject/gvalue.c:311
> #2  0x00007fffe8f4f4be in gst_structure_free (structure=0x7fffd8118300) at
> ../subprojects/gstreamer/gst/gststructure.c:538
> #3  0x00007fffe9fd71db in boxed_clear (self=0x7fffe8c5a980) at
> ../subprojects/pygobject/gi/pygi-boxed.c:51
> #4  boxed_dealloc (self=0x7fffe8c5a980) at
> ../subprojects/pygobject/gi/pygi-boxed.c:69
> #5  0x00007ffff7d29076 in subtype_dealloc () from
> /lib64/libpython3.10.so.1.0
> #6  0x00007fffe9fcc475 in _Py_DECREF (op=<optimized out>) at
> /usr/include/python3.10/object.h:500
> #7  _callable_info_dealloc (self=0x7fffe8c39bf0) at
> ../subprojects/pygobject/gi/pygi-info.c:685
> #8  0x00007ffff7d17b00 in _PyEval_EvalFrameDefault () from
> /lib64/libpython3.10.so.1.0
> #9  0x00007ffff7d118d3 in _PyEval_Vector () from
> /lib64/libpython3.10.so.1.0
> #10 0x00007fffe9fd7d41 in _pygi_closure_handle (cif=<optimized out>,
> result=<optimized out>, args=<optimized out>, data=<optimized out>) at
> ../subprojects/pygobject/gi/pygi-closure.c:582
> #11 0x00007ffff7fb0322 in ffi_closure_unix64_inner () from
> /lib64/libffi.so.8
> #12 0x00007ffff7fb0968 in ffi_closure_unix64 () from /lib64/libffi.so.8
> #13 0x00007fffe9182bc1 in _execute_op (op=0x555555aca3a0) at
> ../subprojects/gst-plugins-bad/ext/webrtc/gstwebrtcbin.c:1007
> #14 0x00007fffe9ecc19f in g_main_dispatch (context=0x7fffd8000b70) at
> ../subprojects/glib/glib/gmain.c:3417
> #15 g_main_context_dispatch (context=0x7fffd8000b70) at
> ../subprojects/glib/glib/gmain.c:4135
> #16 0x00007fffe9ecc528 in g_main_context_iterate (context=0x7fffd8000b70,
> block=block at entry=1, dispatch=dispatch at entry=1, self=<optimized out>) at
> ../subprojects/glib/glib/gmain.c:4211
> #17 0x00007fffe9ecc7cf in g_main_loop_run (loop=0x7fffd8002580) at
> ../subprojects/glib/glib/gmain.c:4411
> #18 0x00007fffe9185146 in _gst_pc_thread (webrtc=0x555555ac4120) at
> ../subprojects/gst-plugins-bad/ext/webrtc/gstwebrtcbin.c:928
> #19 0x00007fffe9ef4fad in g_thread_proxy (data=0x555555685300) at
> ../subprojects/glib/glib/gthread.c:827
> #20 0x00007ffff788ce2d in start_thread () from /lib64/libc.so.6
> #21 0x00007ffff7912620 in clone3 () from /lib64/libc.so.6
> (gdb) c
> Continuing.
> INFO     __main__:answer: <GstWebRTC.WebRTCSessionDescription object at
> 0x7fffe8c5a9e0 (GstWebRTCSessionDescription at 0x7fffd8116760)>
> INFO     __main__:answer fields: <enum 669822870 of type
> GstWebRTC.WebRTCSDPType>
> INFO     __main__:answer fields: <enum 669822870 of type
> GstWebRTC.WebRTCSDPType> 669822870
> INFO     __main__:answer fields: <enum 669822870 of type
> GstWebRTC.WebRTCSDPType> unknown
> INFO     __main__:answer sdp is None: True
> INFO     __main__:answer fields: None
> Traceback (most recent call last):
>
> Cheers
> -Matt
>
> On 6/7/22 20:55, Alexei Golovko wrote:
>
> `apt show python3-gst-1.0` gives me version 1.20.1
>
> Also I made a minimal example without external dependencies: just set
> hardcoded SDP as local-description and emit create-answer.
> https://pastebin.com/9xPk6EkY
> It also prints unknown SDP type, new enum value each run:
> https://pastebin.com/zKhDsLZZ
>
> This behaviour also reproduces with python 3.9 on NixOS 22.05 (I've used
> the following shell.nix: https://pastebin.com/vsBG5RXR).
>
> вт, 5 июл. 2022 г. в 17:33, Matthew Waters <ystreet00 at gmail.com>:
>
>> Looks like you are looking for python3-gst-1.0:
>> https://packages.ubuntu.com/search?suite=default&section=all&arch=any&keywords=python3-gst&searchon=names
>> .
>>
>> I don't know how exactly the python bindings operate so cannot give you
>> that information.  Others on this list may be able to point you in the
>> right direction.
>>
>> On 5/7/22 23:19, Alexei Golovko wrote:
>>
>> I have installed python3-gi package from apt repository, version
>> 3.42.0-3build1.
>> Yes, value for the enum changes each run.
>> Could you give advice on how to check if this is a python binding problem
>> or lower-level one?
>>
>> вт, 5 июл. 2022 г. в 16:02, Matthew Waters <ystreet00 at gmail.com>:
>>
>>> Please keep the list in CC so others searching for the same issue might
>>> find a solution.
>>>
>>> PyGObject is not gst-python.  gst-python provides some convenience API
>>> on top of PyGObject and may be required in this case.
>>>
>>> That log is expected for your case (no existing transceiver or pad).
>>>
>>> The value for the enum is different from your last run.  This points to
>>> uninitialized/random memory being accessed.  You would need to figure out
>>> if that's in the python translation layer or not.
>>>
>>> Cheers
>>> -Matt
>>>
>>> On 5/7/22 22:41, Alexei Golovko wrote:
>>>
>>> Here is the log with GST_DEBUG=3,*webrtc*:7 —
>>> https://pastebin.com/RshtnqQx
>>> I use PyGObject 3.42.1.
>>>
>>> I see in logs following lines:
>>> 2022-07-05 15:15:57.949 jord ERROR| 0:00:01.214992971     9
>>> 0x55e2cbd19980 DEBUG              webrtcbin
>>> gstwebrtcbin.c:1874:_find_codec_preferences:<webrtctransceiver0> Could not
>>> find caps for mline 0
>>> 2022-07-05 15:15:57.949 jord ERROR| 0:00:01.215007126     9
>>> 0x55e2cbd19980 TRACE              webrtcbin
>>> gstwebrtcbin.c:4071:_create_answer_task:<wrb> trying to compare
>>> application/x-rtp, media=(string)video, payload=(int)96,
>>> clock-rate=(int)90000, encoding-name=(string)H264,
>>> profile-level-id=(string)42e01f, packetization-mode=(string)1,
>>> rtcp-fb-nack=(boolean)true, rtcp-fb-nack-pli=(boolean)true,
>>> rtcp-fb-goog-remb=(boolean)true; application/x-rtp, media=(string)video,
>>> payload=(int)97, clock-rate=(int)90000, encoding-name=(string)RTX,
>>> apt=(string)96 and (NULL)
>>>
>>> Maybe they are related to the problem, though I am not sure.
>>>
>>> вт, 5 июл. 2022 г. в 15:12, Matthew Waters <ystreet00 at gmail.com>:
>>>
>>>> Hi,
>>>>
>>>> That SDP doesn't actually exist as a valid value.  You can enable
>>>> GStreamer debugging with GST_DEBUG=3,*webrtc*:7 and that may show
>>>> something interesting.
>>>>
>>>> Otherwise, one has to figure out if the python bindings are doing
>>>> something weird here.  I assume you have a relevant gst-python
>>>> installation available and in use.
>>>>
>>>> Cheers
>>>> -Matt
>>>>
>>>> On 5/7/22 02:44, Alexei Golovko via gstreamer-devel wrote:
>>>> > Hi,
>>>> > I try to use webrtcbin with Janus.
>>>> > I've found examples like
>>>> >
>>>> https://github.com/centricular/gstwebrtc-demos/blob/master/janus/janusvideoroom.py
>>>> ,
>>>> >
>>>> https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/blob/master/tests/examples/webrtc/webrtcrenego.c
>>>> ,
>>>> >
>>>> https://github.com/centricular/gstwebrtc-demos/blob/master/sendrecv/gst-rust/src/main.rs
>>>> ,
>>>> >
>>>> https://gitlab.freedesktop.org/gstreamer/gst-examples/-/blob/master/webrtc/sendrecv/gst/webrtc_sendrecv.py
>>>> .
>>>> >
>>>> > They tend to create an offer locally, send it to Janus, receive an
>>>> > answer and set it as a remote description. I would like to mimic
>>>> > behaviour, which we used to use with python's aiortc: get an offer
>>>> > from Janus, generate an answer and send it back.
>>>> >
>>>> > I set SDP offer from Janus with set-remote-description, then emit
>>>> > create-answer; but I get an answer WebRTCSessionDescription with an
>>>> > empty SDP and a very strange WebRTCSDPType=-43384639 (non-existing
>>>> enum?).
>>>> >
>>>> > What am I doing wrong and how to fix this?
>>>> >
>>>> > The python script used is here: https://pastebin.com/WGPcF64m
>>>> > Module dvr_processor.dvr_processor.janus contains communication with
>>>> > Janus: https://pastebin.com/KAhTv8Lq
>>>> > Logs are here: https://pastebin.com/QVegDhRZ
>>>> >
>>>> > It is gstreamer 1.20.1 on ubuntu-22.04 based image.
>>>> >
>>>> > Regards,
>>>> > Alexei Golovko.
>>>>
>>>>
>>>
>>
>
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