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Multicast address is not properly cached

There is an issue with multicast address usage. Modify examples/test-multicast.c so that:

  • Only the audio part is exposed in the factory (comment out the video part)
  • Force the pool to only use one address and a single port pair:
   gst_rtsp_address_pool_add_range (pool, "224.3.0.1", "224.3.0.1", 5000, 5001, 16);

We should therefore get the audio stream via 224.3.0.1:5000, but gst-rtsp-server fails hard.

What happens is the following:

  • When the SDP is constructed, the code in question calls gst_rtsp_stream_get_multicast_address() which will return the cached multicast address. If none are available, it will request it from the address pool (via gst_rtsp_address_pool_acquire_address) and cache it. It properly returns 224.3.0.1:5000 (with 2 ports).
  • Later on when the SETUP request is handled, the transport is configured (default_configure_client_transport() from rtsp-client.c), which calls gst_rtsp_stream_allocate_udp_sockets().
  • That code calls alloc_ports_one_family() ... and this is where things go wrong

That function does not check whether we already have a cached address (which we do) and therefore calls gst_rtsp_address_pool_acquire_address() again ... which fails.

If we already have a cached address, we should use that.