Split screen

Problem

Compare two video files by using a vertical split screen.

Solution

ffmpeg \
    -i input_file_1 \
    -i input_file_2 \
    -filter_complex \
        "[0]crop=iw/2:ih:0:0[left]; \
         [1]crop=iw/2:ih:iw/2:0[right]; \
         [left][right]hstack[out]" \
    -map "[out]" \
    output_file

Command syntax

ffmpeg

starts the command

-i input_file_1

path, name and extension of the first input files

-i input_file_2

path, name and extension of the second input files

-filter_complex

A complex filter graph is needed:

• the first input file is cropped vertically to the left half;
• the second input file is cropped vertically to the right half;
• the two half images are stacked horizontally to a full image.

-map "[out]"

maps the [out] stream to the output

output_file

path, name and extension of the output file

Discussion

A split screen is useful for comparing files with big differences, while for comparing files with little differences a delta file is more useful.

The different filters of a filter chain are divided by a comma (,) which is not used in this case. The different filter chains of a filter graph are divided by a semi-colon (;). If the whole filter graph is put into quotation marks, then spaces can be added after , and ; for readability reasons.

The mapping is not necessary in this case, because it’s implicit.

Exercises

• horizontal split screen
• split screen with a tiny black line between the two sectors

2020-11-22