Receiving RTP without udpsrc

[wsnark at tuta.io]

Hi,

I'm trying to build a GStreamer-based RTP receiver in a sandboxed architecture:
- A "listener" process listens at UDP port and redirect the stream to receiver
- "Receiver" process runs in a sandbox without network access, gets data from "listener" over a pipe.

The reason for such architecture is increased security - so that vulnerable parsing code is run with minimum privileges.

At prototyping phase I'm trying to create a PoC using "gst-launch-1.0", but I cannot find a way to create a working pipeline to play RTP stream from a pipe instead of udpsrc.

For example, usual udpsrc receiving pipeline that works:
gst-launch-1.0 udpsrc  port=3000 caps="application/x-rtp, media=(string)audio, clock-rate=(int)8000, encoding-name=(string)PCMU" ! rtppcmudepay ! mulawdec ! pulsesink

Corresponding sending part is 
gst-launch-1.0 filesrc location="test.wav" ! wavparse ! audioconvert ! audioresample ! mulawenc ! rtppcmupay ! udpsink host=127.0.0.1 port=3000

Changing udpsrc to filesrc doesn't work:
gst-launch-1.0 filesrc location="/tmp/pipe" !  "application/x-rtp, media=(string)audio, clock-rate=(int)8000, encoding-name=(string)PCMU" ! rtppcmudepay ! mulawdec ! pulsesink

Sending part: 
gst-launch-1.0 filesrc location="test.wav" ! wavparse ! audioconvert ! audioresample ! mulawenc ! rtppcmupay ! filesink location=/tmp/pipe

The stream is actually played, but just garbled sound. Error output:
WARNING: from element /GstPipeline:pipeline0/GstRtpPcmuDepay:rtppcmudepay0: Could not decode stream.
Additional debug info:
gstrtpbasedepayload.c(503): gst_rtp_base_depayload_handle_buffer (): /GstPipeline:pipeline0/GstRtpPcmuDepay:rtppcmudepay0:
Received invalid RTP payload, dropping

If I capture incoming stream to file, then I'm unable to play it either (same behavior). If I remove RTP elements from the pipeline, raw PCMU is played fine.

So my questions are:
1. Is it possible to play RTP stream without udpsrc using gst-launch-1.0?
2. Is it possible to implement this in code, in own application?

Thanks,
Wire Snark

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