Comskip users rejoice.  Comskip now supports live detection.  If you're using 1.2.0.9 everything will work, you just need to configure dtb for live detection (the first step); you may want to download the latest rev of comskip there was a relevant bug fix.  None of this would be possible without Erik's (comskip author) effort, so if you use comskip and find this feature valuable think about thanking him for the $20 he saved you.

Other versions can do it to but it's a little more work.

• download the latest rev (0.79.111)
• extract it to the DTB applications directory (usually %programfiles%\dvrmstoolbox\applications)
• open comskip.ini in your favorite text editor and change/add the following lines
• verbose=0 (optional)
• delete_logo_file=1 (optional)
• live_tv=1
• live_tv_retries=120 300 (600 may be required for low quality SD ATSC)  
  
• output_dvrmstb=1
• dvrmsstandoff=120000
• create a new profile in the DTB settings tool for comskip
  
• add the ComskipAdvanced and FWThrottle actions
  
• Configure it to scan the input file, and enter the full path to the commercial xml files
  
• Order FWThrottle above ComskipAdvanced, name the profile and save it
  
• Go to the Processing Tab in the settings tool and select the new profile.  Click "Save" to exit the tool
  
• Open the PC tool and change the "Every File" PC to use the new profile
  
  

 If you need to incorporate this into profile that do more advanced things, just add the ComskipAdvanced action before the FindCommercials (leave FindCommercials it will read the xml file created by comskip and not run comskip again) action, and check "ContinueOnFail".