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04-add-and-remove-network-source.md

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Adding and Removing RTP-Sources

As a more realistic example of adding and removing Sources to a playing Pipeline, this Example creates a Pipeline with an audiotestsrc and an audiomixer. After a while, a Bin (a Cluster of Elements) which receives and decodes Audio coming from the Network via RTP is created, added to the Pipeline and linked to the audiomixer. After 4 and 6 seconds additional Bins of this kind are created and also linked. Then, again with 2 Seconds in between, the Source-Bins are removes again, before thw whole process starts over again.

Network-Sources can, for example. look like the following Pipeline. If you want, you can start such Pipelines on different Computers across the Network, just adjust the destination IP-Address.

gst-launch-1.0 audiotestsrc freq=220 is-live=true ! \
  audio/x-raw,format=S16BE,rate=48000,channels=2 ! \
  rtpL16pay ! \
  application/x-rtp,clock-rate=48000,media=audio,encoding-name=L16,channels=2 ! \
  udpsink host=127.0.0.1 port=10000

You should read Adding RTP Network-Sources and Adding and Removing Sources before this, because important Aspects that have been explained there are not repeated here.

The most important new Lines have been marked as such:

  1. In this Example we create a Bin to collect all the Elements that comprise the RTP-Source and manage them together. This also helps avoid some of the Problems described in Adding and Removing Sources. We also give the bin a unique name, so that it can be found by name again later. We could also store the Reference to the bin, depending on the use-case.

  2. We selecl the Src-Pad of the last Element in the Bin and explicitly create a Ghost-Pad for it. This pad is added as Src-Pad to the Bin.

  3. Because the Bin now has an unlinked Src-Pad, we can just use Element.link to link it to the Audio-Mixer.

  4. Upon removing we select the Bin's src-Pad by its name and thr select the Pad's Peer - which we know is the Mixer-Pad. This reference is kept for releasing the Mixer-Pad later.

  5. Before removing the Bin we set its State to NULL. This propagates the State-Change to its Children in the correct order. Then the Bin is removed, which removes all of its Children, too. Finally the requested Mixer-Pad is released.