Why do I get a black box when I tile pictures with -filter_complex tile=2x1 in FFmpeg?

Question

As I was trying to write a script (which attempts to join two pictures eventually) using FFmpeg I came across a very weird behaviour.

This is a command from I've found in the How to join two images into one with FFmpeg? thread:

ffmpeg -i a.jpg -i b.jpg -filter_complex scale=120:-1,tile=2x1 output.jpg

• Input: a.jpg, b.jpg

  

• Output: output.jpg

  

What happened to the B cat? Why is it missing from the output image? I couldn't find any information why tile=2x1 behaves like this.

Answer 1

The tile filter is when one wants to

Tile several successive frames together.

To stack two frames horizontally, use

ffmpeg -i a.jpg -i b.jpg -filter_complex [1]scale=120:-1[b];[0][b]hstack output.jpg