youtube-dl/devscripts/bash-completion.in

__youtube-dl()
{
    local cur prev opts
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    opts="{{flags}}"

    if [[ ${cur} == * ]] ; then
        COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
        return 0
    fi
}

complete -F __youtube-dl youtube-dl