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11

Importing and Exporting RTP Media Streams

Many applications need to be able to read and write RTP streams. For example, conferencing application might record a conference and broadcast it at a later time, or telephony applications might transmit stored audio streams for announcement messages or hold music.

You can save RTP streams received from the network to a file using an RTP file writer DataSink. Similarly, you can read saved files and either present them locally or transmit them across the network.

Reading RTP Media Streams from a File

To read data from a file and present or transmit it, you can use a MediaLocator that identifies the file to construct a DataSource, or use the MediaLocator to directly construct your Processor. The file types that can be used for RTP transmissions depend on what codec plug-ins you have available to transcode and packetize the data into an RTP-specific format.

Example 11-1: Reading RTP streams from a file (1 of 3)
         // Create a Processor for the selected file. Exit if the 
         // Processor cannot be created.
         try { 
             String url= "file:/home/foo/foo.au";
 
             processor 
               = Manager.createProcessor( new MediaLocator(url)); 
         } catch (IOException e) { 
             System.exit(-1); 
         } catch (NoProcessorException e) { 
             System.exit(-1); 
         } 
         
         // configure the processor
         processor.configure(); 
 
         // Block until the Processor has been configured 
 
         TrackControl track[] = processor.getTrackControls(); 
         
         boolean encodingOk = false;
         
         // Go through the tracks and try to program one of them to
         // output ulaw data. 
         for (int i = 0; i < track.length; i++) { 
             if (!encodingOk && track[i] instanceof FormatControl) { 
                        
                 if (((FormatControl)track[i]).
                     setFormat( new AudioFormat(AudioFormat.ULAW_RTP, 
                                                8000, 
                                                8, 
                                                1)) == null) {
 
                     track[i].setEnabled(false); 
                 }
                 else {
                     encodingOk = true; 
                 }
             } 
             else { 
                 // we could not set this track to ulaw, so disable it 
                 track[i].setEnabled(false); 
             } 
         }
         
         // At this point, we have determined where we can send out 
         // ulaw data or not. 
         // realize the processor 
         
         if (encodingOk) { 
             processor.realize(); 
             
             // block until realized. 
             // get the output datasource of the processor and exit 
             // if we fail 
             DataSource ds = null;
             
             try { 
                 ds = processor.getDataOutput(); 
             } catch (NotRealizedError e) { 
                 System.exit(-1);
             }
             // hand this datasource to manager for creating an RTP 
             // datasink.
             // our RTP datasink will multicast the audio 
             
             try {
                 String url= "rtp://224.144.251.104:49150/audio/1";
 
                 MediaLocator m = new MediaLocator(url);
 
                 DataSink d = Manager.createDataSink(ds, m);
 
                 d.open();
                 d.start(); 
             } catch (Exception e) {
                 System.exit(-1);
             }
         }

Exporting RTP Media Streams

RTP streams received from the network can be stored as well as presented. To write the data to a file, you retrieve the DataSource from the ReceiveStream and use it to create a file writing DataSink through the Manager.

If you want to transcode the data before storing it, you can use the DataSource retrieved from the ReceiveStream to construct a Processor. You then:

  1. Set the track formats to perform the desired encoding.
  2. Get the output DataSource from the Processor.
  3. Construct an RTP file writer with the DataSource.

In the following example, whenever a new stream is created in the session:

  1. The stream is retrieved from NewReceiveStreamEvent.
  2. The DataSource is acquired from the ReceiveStream.
  3. The DataSource is passed to the Manager.createDataSink method along with a MediaLocator that identifies the file where we want to store the data.

This example handles a single track. To write a file that contains both audio and video tracks, you need to retrieve the audio and video streams from the separate session managers and create a merging DataSource that carries both of the streams. Then you hand the merged DataSource to Manager.createDataSink.

Example 11-2: Writing an RTP stream to a file
     public void update(ReceiveStreamEvent event) {
         // find the source session manager for this event
         SessionManager source = (SessionManager)event.getSource();
        
         // create a filewriter datasink if a new ReceiveStream 
         // is detected
         if (event instanceof NewReceiveStreamEvent) {
             String cname = "Java Media Player";
             ReceiveStream stream = null;
             
             try {
                 // get the ReceiveStream
                 stream =((NewReceiveStreamEvent)event)
                         .getReceiveStream();
 
                 Participant part = stream.getParticipant();
 
                 // get the ReceiveStream datasource
                 DataSource dsource = stream.getDataSource();
 
                 // hand this datasource over to a file datasink
                 MediaLocator f = new MediaLocator("file://foo.au");
 
                 Manager.createDataSink(dsource, f);    
             } catch (Exception e) {
                 System.err.println("newReceiveStreamEvent exception " 
                                    + e.getMessage());
                 return;
             }
         }
     }



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