Set the audio 'original duration' during initial events parsing

This is the point at which the start/stop events for the audio are
correctly matched up with eachother; doing it later can give
incorrect results if an 'end recording' event was missing from
the events file.

record-and-playback/core/lib/recordandplayback/generators/audio.rb

@@ -237,6 +237,7 @@ module BigBlueButton
           filename = event.at_xpath('filename').text
           filename = "#{audio_dir}/#{File.basename(filename)}"
           if audio_edl.last[:audio] && audio_edl.last[:audio][:filename] == filename
+            audio_edl.last[:original_duration] = timestamp - audio_edl.last[:timestamp]
             audio_edl << {
               :timestamp => timestamp,
               :audio => nil

record-and-playback/core/lib/recordandplayback/generators/events.rb

@@ -339,8 +339,6 @@ module BigBlueButton
         else
           edl_entry[:duration] = edl[i+1][:timestamp] - edl_entry[:timestamp]
         end
-        # the original_duration is used to calculate the speed of the output file
-        edl_entry[:original_duration] = edl_entry[:duration]
       end
 
       BigBlueButton.logger.debug "edl with duration:\n#{BigBlueButton.hash_to_str(edl)}"