When you submit an encoding job in the WiretapCentral UI, the WiretapCentral ffmpeg encoder is called with a series of command-line parameters, depending on the codec preset and quality level selected in the Export window.

These presets are stored in the export_presets.xml file, located at /var/www/html/wiretapcentral/presets/ on the Smoke server machine.

Each preset defines the audio and video encoding format and parameters, as well as the video encoding quality.

WiretapCentral provides a number of useful default presets. Advanced users are encouraged to add new presets, or modify existing presets to better suit their needs.

To modify encoding presets:

1. Open a terminal to the WiretapCentral server machine, and log in as root.
2. Open the file /var/www/html/wiretapcentral/presets/export_presets.xml in a text editor, such as nano.
   • Each encoding preset is defined by a <preset> node in the XML file.
   • Each <preset> node has an <audio> child node that defines the audio codec parameters, and a <video> child node that defines the video codec parameters.
   • <audio> nodes have a <base> child node that defines audio encoding parameters.
   • <video> nodes have a <base> child node that defines most of the video encoding parameters, as well as a number of <quality> child nodes that define the steps of the Quality slider in the Export window for that preset.
3. Modify the parameters in the <base> nodes, as well as the number and values of <quality> nodes. The number of <quality> nodes in the XML file for a preset will be reflected by the number of steps in the Quality slider for the respective preset.
4. Save and close the export_presets.xml file, and refresh the Web browser that points to WiretapCentral.

If an encoding job fails without a clear error message after you have modified export preset settings, perform the following procedure to obtain detailed error information from the codec.

To troubleshoot clip encoding:

1. In the Export window, click View Presets.

   A new browser window opens to the http://<hostname_or_IP>/wiretapcentral/export/<session_name>/ URL.

   Where <session_name> is the name of the failed export job.

   The list of files in the export session is displayed, including a file named info.txt .

2. Click the info.txt file.

   The browser displays the contents of the file.

3. Locate the “Full command (execute as apache or root):” line at the end of the file.

   The next line in the file contains the command and parameters that were sent by WiretapCentral to the codec when attempting to encode the clip.

4. Select the entire line and copy it to the clipboard.
5. Log into the WiretapCentral server machine as root, paste the command, and run it.

   The codec outputs detailed messages on the reason for the failure.

6. Refer to online ffmpeg discussion groups for information on how to troubleshoot the reported problems.