Tech Tips - Active Format Description (AFD)

Overview

PixelTools products can add content Active Format Description (AFD) headers to your video during encoding or to an existing MPEG stream without transcoding.

Active Format Description is a standard set of codes that can be sent in the MPEG video stream or in the baseband SDI video signal that carries information about their aspect ratio and active picture characteristics.

It is used by television broadcasters to enable both 4:3 and 16:9 television sets to optimally present pictures transmitted in either format. It has also been used by broadcasters to dynamically control how down-conversion equipment formats widescreen 16:9 pictures for 4:3 displays.

Demo of Active Format

Download the AfdTrial.zip to obtain a demo version of MPEGRepairHD that is configured to automatically add Active Format Description headers during encoding.

Unzip the demo file into a directory and run the AFD.bat file to launch the demo. The demo will automatically add the 16:9 Center AFD flags during encoding. You can view the resultant AFD data in the user_data in the MPEGRepairHD decode statistics window.

Adding Active Format Description during encoding

The Active Format Description, specific to your source video, can be added to elementary video user_data during encoding with MPEGRepairHD or ExpertHD. Select the Optimize Encode | Configure | Line 21 dialog to bring up the Active Format Description selection dialog. Check the Add AFD Flags and select your desired AFD mode from the drop down menu. During encoding, your selected AFD header will be periodically added to the stream.

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Adding Active Format Description an existing MPEG stream

Select your elementary video stream that you wish to insert content advisory flags into in the MPEG Decode “File to Decode or Analyze” edit box. Then check the Decode | Configure | Fix Stream | Insert Active Format Description and select your desired AFD option from the drop down menu. Enter the name of your resultant file in the “Save Fixed File” edit box and depress the Decode Run on the GUI. Your selected file will have AFD user_data added at appropriate intervals and the resultant video file will be saved as the “Save Fixed File”.

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Specifications

The Active Format Description is defined in the ATSC Standard A/53. This header should be included in encoded video when “the rectangular picture area containing useful information does not extend to the full height or width of the coded frame.”

The following Active Format Descriptions are supported by PixelTools products:

box 16:9 top

box 14:9 top

box > 16:9 center

Active format same as coded frame

4:3 center

16:9 center

14:9 center

4:3 with shoot and protect 14:9 center

16:9 with shoot and protect 14:9 center

16:9 with shoot and protect 4:3 center

MPEGRepairHD and ExpertHD are trademarks of PixelTools Corporation. All other brand names are trademarks or registered trademarks of their respected holders