Debugging Macroblocks and Motion Vectors

You can use ffmpeg or ffplay to analyze motion vectors in a video file.

Previous versions of ffmpeg (pre-October 2017) allowed you to analyze macroblocks too, but this option was removed.

The ​`codecview` filter can be used to show motion vectors as small arrows for each macroblock. It takes one option called mv, which specifies the type of motion vector to be drawn:

• pf – forward predicted motion vectors of P pictures
• bf – forward predicted motion vectors of B pictures
• bb – backward predicted motion vectors of B pictures

For example, you can use:

ffplay -flags2 +export_mvs input.mp4 -vf codecview=mv=pf+bf+bb
ffmpeg -flags2 +export_mvs -i input.mp4 -vf codecview=mv=pf+bf+bb output.mp4

Example:

Caveats:

• Earlier versions of ffmpeg do not have this filter, but support the now deprecated -vismv option.
• This option does not work for codecs which do not export motion vectors (most non-MPEG based codecs)