Using UDP Multicast with GStreamer
In this document you will find how to create a network connection using multicast in order for transmit audio and/or video streaming.
Audio Multicast Streaming
In this section it will be shown how to build a GStreamer pipe for transmit audio information through a multicast network.
The pipes used are the following
gst-launch-0.10 filesrc location=<file.mp3> ! mad ! audioconvert ! audioresample ! mulawenc ! rtppcmupay ! udpsink host=<multicast IP address> auto-multicast=true port=<port number>
gst-launch-0.10 udpsrc multicast-group=<multicast IP address> auto-multicast=true port=<port number> caps="application/x-rtp" ! rtppcmudepay ! mulawdec ! alsasink
On the server side we first used a filesrc element to set the media audio file we will play (this pipe is only for MP3 audio files), then the file content is passed through a mad decoder in order to get the audio in raw format. Once the audio has been decoded, we pass it through an audioconvert and an audioresample, those convert the audio to raw audio with a sample rate of 8KHz which is the sample rate necessary to decode the audio to mu-law using the mulawdec element.
Before we send the audio through the network it is necessary to package it into a rtp package with the correct payload, that is doing by using rtppcmupay.
Finally the audio packages are sent to the network by using the udpsink element. In order to configure the connection as a multicast type it is necessary to activate the udpsink's multicast compatibility and set the multicast IP address and port (from 1024 to 65535).