How to generate wav file from RTP flow

This page describes the way to generate a wav file from the RTP flow recorded over an Ethernet interface. The requirement is done by using the "Analog" properties in the Clarinet filter used on-line (filter name defined in the profile) or off-line (Filter-Run Protocol).

Setting the test conditions

The connections of Clarinet-Book USB units and the settings of test conditions for a basic VOIP communication are detailed in the following pages:

Setting the test conditions for VOIP / Analog filter

The protocol filter file Lan_auto_rtp_analog.acf (created with the Wizard from the Template list) specifies the stack of protocol.

As the IP protocols are automatically detected by the protocol value, the stack defined in the "Protocol specification" has the layers D3 to D7 set to "Automatic". The RTP protocol is decoded at the level 5, the "analog" protocol is added to the level 6.

The"Analog Measurement" tab of the filter includes specifications for both functions: wav files generation and QoS measurement. The filter file Lan_auto_rtp_analog.acf  is configured only to generate the wav files..

  • Modifications of the filter to apply in "Received Voice" part:
    • the codec specifications must correspond to the value set in the PT of the RTP messages.
      For information:
      • PT=000 è G711 mLaw
      • PT=008 è G711 ALaw
      • PT=018 è G729
    • the output file must specify:
      • the file name (default= Rtp_analog.wav)
      • the encoding specifications of the file.wav
  • the quality measurement should be set to "Off" if the purpose is only to generate the wav files.

Generating the Wav file

The wav files are automatically created in the working directory: with the basename defined in the filter file (Rtp_analog_xx.wav as an example). Source and destination IP addresses are added to the basename.

Applying the filter conditions

The processing of the events can be done:

  • off-line by using Filter èRun Protocol:
    • source file including the RTP flow (Lan_mon.ace as an example).
    • filter name (Lan_auto_rtp_analog.acf  as an example)
    • result file.generated (Lan_mon_rlt.ace as an example).
  • on-line, at the end of the profile execution, with the following settings:
    • configuration file set as WI_ANALOG by Clarinet-Init
    • filter name defined in the profile to be executed
 
Related topic:
Generation of Analog events
Analog filter specifications
 

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updated:  27-Feb-04