基于DeepStream搭建GStreamer RTSP ONVIF服务器无报错但无法拉流求助

我以DeepStream SDK的deepstream-test1-rtsp-out示例为基础开发，原示例的RTSP服务器可正常推送视频，能通过VLC打开流。原RTSP服务器代码片段如下：

# Start streaming
rtsp_port_num = 8554
    
server = GstRtspServer.RTSPServer.new()
server.props.service = "%d" % rtsp_port_num
server.attach(None)
    
factory = GstRtspServer.RTSPMediaFactory.new()
factory.set_launch( "( udpsrc name=pay0 port=%d buffer-size=524288 caps=\"application/x-rtp, media=video, clock-rate=90000, encoding-name=(string)%s, payload=96 \" )" % (updsink_port_num, codec))
factory.set_shared(True)
server.get_mount_points().add_factory("/ds-test", factory)
    
print("\n *** DeepStream: Launched RTSP Streaming at rtsp://localhost:%d/ds-test ***\n\n" % rtsp_port_num)

我尝试将其改为RTSP ONVIF服务器，运行时未出现GStreamer报错，但无法打开流。测试代码如下：

rtsp_port_num_onvif = 8554
server1 = GstRtspServer.RTSPOnvifServer.new()
server1.props.service = "%d" % rtsp_port_num_onvif
server1.attach(None)

factory1 = GstRtspServer.RTSPOnvifMediaFactory.new()
factory1.set_backchannel_launch("( udpsrc name=pay0 port=%d caps=\"application/x-rtp, media=video, clock-rate=90000, encoding-name=(string)%s, name=depay_backchannel, payload=96\ ! rtph264depay name=depay0 ! fakesink async=false")" % (updsink_port_num, codec))
factory1.set_shared(False)
server1.get_mount_points().add_factory("/ds-test-onvif", factory1)

print("\n *** DeepStream: Launched RTSP Onvif Streaming at rtsp://localhost:%d/ds-test-onvif ***\n\n" % rtsp_port_num_onvif)

查阅GStreamer的RTSP Server文档后，相关要点如下：

• GstRtspServer.RTSPOnvifServer与GstRtspServer.RTSPServer的唯一区别是前者会创建GstRtspServer.RTSPOnvifClient，该客户端支持ONVIF特定功能，比如允许客户端向服务器回传媒体的反向通道。
• RTSP ONVIF Media Factory的set_backchannel_launch函数：当前支持的特殊ONVIF功能是反向通道，允许客户端在常规PLAY媒体中向服务器回传媒体；传入的管道需包含名为depay_backchannel的解封装器，解封装器接收端的caps需指定负载类型、时钟速率和编码名称；管道必须以设置了async=false的接收器结尾，否则媒体无法准备。

请问该如何修改代码才能让RTSP ONVIF服务器正常推流？

内容的提问来源于stack exchange，提问作者CYrOgAV