How to use gstreamer rtspsrc to display a rtsp source?

Question

I'm playing with gstreamer rtsp.

I created a rtsp sink as this:

gst-launch-1.0 videotestsrc ! x264enc ! rtph264pay config-interval=10 pt=96 ! udpsink host=127.0.0.1 port=5000

I can't open it directly by VLC (with rtsp://127.0.0.1:5000) but with a vlc.sdp file, it can be displayed. the vlc.sdp file is like:

v=0
m=video 5000 RTP/AVP 96
c=IN IP4 127.0.0.1
a=rtpmap:96 H264/90000

vlc vlc.sdp

The file above is copied from somewhere, I don't understand it well but I think the rtsp sink is and working. I think it's rtsp over udp since I see rtph264pay and udpsink in the cmd line above.

Then I'd like to use rtspsrc to display it.

gst-launch-1.0 rtspsrc location=rtsp://127.0.0.1:5000 ! rtph264depay ! avdec_h264 ! autovideosink sync=false

But I have errors like this:

Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Progress: (open) Opening Stream
Progress: (connect) Connecting to rtsp://127.0.0.1:5000
ERROR: from element /GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0: Could not open resource for reading and writing.
Additional debug info:
gstrtspsrc.c(7469): gst_rtspsrc_retrieve_sdp (): /GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0:
Failed to connect. (Generic error)
ERROR: pipeline doesn't want to preroll.
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
Freeing pipeline ...

So what's wrong with my rtspsrc command?

Answer 1

You are not using RTSP on the sending side. You are sending just RTP. I recommend some reading on RTP, RTSP and SDP so you understand how these interact with each other.

TL;DR RTSP is used to initiate a RTP session. Basically it transfers a SDP file to the client with required information on how to receive the RTP stream.

These are 3 different protocols you have to follow if you want a complete RTSP spec required transmission.

Note that GStreamer project has some RTSP libraries too for handling such situations.