How to Separate Interlaced Video Fields in FFmpeg

This guide explains how to use the separatefields filter in FFmpeg to split interlaced video footage into individual, sequential frames. You will learn the exact command-line syntax to separate fields, understand how this process affects video dimensions and frame rates, and discover how to output the results as either an image sequence or a new video file.

Understanding the separatefields Filter

Interlaced video contains two fields (odd and even lines) inside a single frame, captured at slightly different points in time. The separatefields filter splits each of these interlaced frames into two distinct, sequential frames.

Because each field contains only half of the vertical lines of the original frame, applying this filter will: * Double the frame rate (e.g., 29.97 fps interlaced video becomes 59.94 fps sequential frames). * Halve the height of the video (e.g., a 1920x1080 video becomes 1920x540).

Command to Export Fields as an Image Sequence

To extract every individual field as a sequential PNG or JPEG image, use the following command:

ffmpeg -i input.mp4 -vf "separatefields" field_%04d.png

Command to Export Fields to a New Video File

If you want to output the separated fields directly into a new video container, run:

ffmpeg -i input.mp4 -vf "separatefields" -c:v libx264 -crf 18 output.mp4

How to Correct the Aspect Ratio (Prevent Squishing)

Because separating fields halves the vertical resolution, the output frames will appear vertically squished. To maintain the original aspect ratio, you can chain the scale filter immediately after separatefields to stretch the height back to its original size:

ffmpeg -i input.mp4 -vf "separatefields,scale=iw:ih" output.mp4