title: Streaming iLBC encoded file via RTP with gstreamer
body: <p>I'm trying to build a gstreamer pipeline to create an RTP audio stream with iLBC codec.  Gstreamer (as of version 0.10) has an RTP payloader pipeline element called <code>rtpilbcpay</code>.  Unfortunately only the RTP packetizing is implemented, the codec itself is not included in gstreamer.  Using the reference code in RFC 3951 I created iLBC encoded files for sample audio that I hoped to be able to use with gstreamer.  However, when I pipe those files into <code>rtpilbcpay</code> I end up with errors.  I "dumbed" down the pipe to the minimum using <code>fakesink</code>, the error is still the same:</p>
  
  <pre><code>~/tmp% gst-launch-0.10 filesrc location=sample.ilbc ! rtpilbcpay ! fakesink
  Setting pipeline to PAUSED ...
  Pipeline is PREROLLING ...
  ERROR: from element /GstPipeline:pipeline0/GstRTPILBCPay:rtpilbcpay0: Element doesn't implement handling of this stream. Please file a bug.
  Additional debug info:
  gstbasertpaudiopayload.c(909): gst_base_rtp_audio_payload_handle_buffer (): /GstPipeline:pipeline0/GstRTPILBCPay:rtpilbcpay0:
  subclass did not configure us properly
  ERROR: pipeline doesn't want to preroll.
  Setting pipeline to NULL ...
  Freeing pipeline ...
  </code></pre>
  
  <p>I'm probably missing a crucial part (file format declaration?) in the pipeline, as I was similarly unable to play back a PCMU encoded file (<code>queue</code> buffers didn't help either):</p>
  
  <pre><code>~/tmp% gst-launch-0.10 filesrc location=sample.pcmu ! mulawdec ! fakesink
  Setting pipeline to PAUSED ...
  Pipeline is PREROLLING ...
  ERROR: from element /GstPipeline:pipeline0/GstFileSrc:filesrc0: Internal data flow error.
  Additional debug info:
  gstbasesrc.c(2550): gst_base_src_loop (): /GstPipeline:pipeline0/GstFileSrc:filesrc0:
  streaming task paused, reason not-negotiated (-4)
  ERROR: pipeline doesn't want to preroll.
  Setting pipeline to NULL ...
  Freeing pipeline ...
  </code></pre>
  
  <p>Is this simply a bug or is the pipeline setup wrong (I hope it's the latter)?  What further "glue" elements do I need in the pipeline?</p>