Handle bus_call messages.

[danisla]

Fixes #89

• Add bus_call handler to start_pipeline which calls self.pipeline.recalculate_latency() for LATENCY type Gst messages.

While the large stream of rtpsession messages with GST_DEBUG:*2 and greater are gone, these messages appear once when the pipeline is first started. They don't seem to affect the pipeline and turning off GST_DEBUG makes them go away, just like the other messages.

0:00:14.825607089 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<rtpfunnel0:src> minimum latency bigger than maximum latency
0:00:14.825625584 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<send_rtp_sink_0:proxypad23> minimum latency bigger than maximum latency
0:00:14.825631635 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<sink_0:proxypad21> minimum latency bigger than maximum latency
0:00:14.825640932 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<rtprtxsend0:src> minimum latency bigger than maximum latency
0:00:14.825646383 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<bin0:src_0> minimum latency bigger than maximum latency
0:00:14.825651823 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<rtpsession0:send_rtp_src> minimum latency bigger than maximum latency
0:00:14.825657563 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<rtpbin:send_rtp_src_0> minimum latency bigger than maximum latency
0:00:14.825663484 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<rtp_sink:proxypad9> minimum latency bigger than maximum latency
0:00:14.825668504 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<rtp_sink_0:proxypad8> minimum latency bigger than maximum latency
0:00:14.825673383 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<srtpenc0:rtp_src_0> minimum latency bigger than maximum latency
0:00:14.825678733 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<clocksync_0:src> minimum latency bigger than maximum latency
0:00:14.825691336 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<funnel0:src> minimum latency bigger than maximum latency
0:00:14.825699351 25768 0x7f46980d3840 ERROR               GST_PADS gstpad.c:3434:gst_pad_query_latency_default:<dtlssrtpenc0:src> minimum latency bigger than maximum latency

[ehfd]

Perhaps, a bus handler from webrtcbin?
Maybe worth a try.

[danisla]

Perhaps, a bus handler from webrtcbin? Maybe worth a try.

The bus handler should attach to the pipeline, not the bin.

This PR is probably good enough for now wrt to the affected issue.

The gst errors only appear when audio is enabled. However, it doesn't seem to affect the audio.

I suggest creating a new issue for those errors if needed.

[ehfd]

Good enough.

[ehfd]

@danisla I think the core solution is to separate audio and video into different webrtcbins.
When they are in a single stream, the web browser causes #7, whether it is on WebRTC or WebTransport. Hence Parsec a few years ago used WASM Opus decoders (which is an old method).