First, this is a bug mostly for reminder purposes, as I'm not certain the issue is with gst-rtsp-server yet.

Using gst insanity rtsp test (1), which starts a gst-rtsp-server and connects to it using playbin2, sending a seek query to the playbin2 pipeline blocks as the RTP code waits for a reply from the server, which does not come.

The event is sent from PLAYING from a glib timeout or idle source, via gst_element_seek, which never returns. If the pipeline is set to PAUSED before sending the seek query, the query returns, and the pipeline can be put back to PLAYING.

Running the test:
./tests/insanity-test-gst-rtsp --run uri=file://path/to/file/to/stream

I used mostly a webm file, but this happens for all files I tried.

Note that the seek test is currently disabled due to the hang, so this line in tests/insanity-test-gst-rtsp needs uncommenting to reproduce the hang:
  /*{ "seek", &rtsp_test_seek, 0 },*/ /* fails to send event, disabled for now */

It is interesting to note that gst-launch playbin2 uri=rtsp://127.0.0.1:8554/test video-sink='navseek ! autovideosink' does not hang. navseek sends a query as well, but from an event function.

(1) http://cgit.collabora.com/git/user/vincent/insanity-gst/