How do I preserve coloured output when piping to `less -R`?
$ ffmpeg -v debug ...
Coloured output.
$ ffmpeg -v debug ... |& less -R
Dull output.
How do I make the output coloured while piping it to something?
For commands that do not have an option similar to --color=always, you can do, e.g. with your example:
script -c "ffmpeg -v debug ..." /dev/null < /dev/null |& less -R
What script does is that it runs the command in a terminal session.
EDIT: Instead of a command string, if you want to be able to provide an array, then the following zsh wrapper script seems to work:
#!/usr/bin/env zsh
script -c "${${@:q}}" /dev/null < /dev/null |& less -R
As alternative to script, which expectes command line as a string instead of normal array, there is a special mode of reptyr:
reptyr -L ffmpeg -v debug ... < /dev/null |& less -R
Note that not all versions of reptyr have working -L option and accept < /dev/null gracefully. See my pull request for this.