TechTips - Active Format Description (AFD)

Adding Active Format Description (AFD) to video


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 the stream 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 is also used by broadcasters to dynamically control how down-conversion equipment formats widescreen 16:9 pictures for 4:3 displays.

Adding AFD 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.

AFD during encoding

Adding AFD to an Existing Stream

The MPEGRepairHD decode section (left hand side of the GUI) can be used to insert AFD flags into an existing stream without re-encoding. Check the Decode Function Enable Configure | Fix Stream | Insert Active Format Description check box and select your desired AFD format from the associated drop box. Enter the name of the elementary video file that will contain the updated file in the Save Fixed File edit box on the top of the Fix Stream dialog. Close the dialog by depressing the Apply and OK buttons, drop or browse your source video in the File to Decode or Analyze edit box, and depress the Run button to start the process. MPEGRepairHD will process your source video, insert your selected AFD flags periodically in your source video, and save the resultant elementary video as the Save Fixed File name you have selected.

AFD during decoding

Verifying AFD flags in MPEG streams

Expert-Caption or the MPEGRepairHD can be used to verify AFD flags in a MPEG video stream. Drag and drop or browse the file to be analyzed into the File to Decode or Analyze edit box and depress the Analyze button. A dialog will appear that lists the stream properties including the type of AFD flags found if any.

AFD analysis

 

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

Active Format Code Inserted

2                box 16:9 top
3                 box 14:9 top
4                 box > 16:9 center
8                 same as coded format
9                 4:3 center
10               16:9 center
11               14:9 center
13               4:3 protect 14:9 center
14               16:9 protect 14:9 center
15               16:9 protect 4:3 center

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


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