Install ffmpeg with applescript

Ok, try the following script, but see caveats below:

shellScriptHandler("xcode-select --install", false)
shellScriptHandler("sudo chown -R $(whoami) /usr/local/Cellar", true)
shellScriptHandler("ruby -e \"$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)\" <<< " & return, false)
shellScriptHandler("sudo chown -R $(whoami) /usr/local/var/homebrew /usr/local/share/zsh /usr/local/share/zsh/site-functions", true)
shellScriptHandler("/usr/local/Homebrew/bin/brew install ffmpeg", false)
shellScriptHandler("/usr/local/Homebrew/bin/brew install node", false)
shellScriptHandler("sudo chown -R $(whoami) /usr/local/bin /usr/local/etc", true)
shellScriptHandler("/usr/local/bin/npm install --global ffmpeg-progressbar-cli", false)

on shellScriptHandler(command, usesAdmin)
    log command
    (*
        The try block catches any errors and reports them; the user can choose 
        to continue execution if it's a warning, or cancel execution outright.

        The 'eval' statement forces do shell script to read the standard
        interactive $PATH variable, so that it sees /user/local/, otherwise it 
        can't find the files it needs.
    *)
    try
        do shell script "eval `/usr/libexec/path_helper -s`; " & command administrator privileges usesAdmin
    on error errstr
        display dialog errstr buttons {"Continue", "Cancel"} default button "Continue"
    end try
end shellScriptHandler

Caveats:

1. If there is a previous install of homebrew, the first line may fail with a permissions error; on my system, it tried to copy something from the Xcode bundle to /usr/local/Homebrew/.git/..., but needed root privileges. I solved that problem by deleting the folder /usr/local/Homebrew entirely, but that might be a bit drastic for the general case. You'll have to see if the problem recurs.
2. I added a couple of chown commands in lines 2 and 4. These popped up as errors when I ran the ruby script and brew install.... You may run across other such errors based on idiosyncrasies in different systems, but it shouldn't hurt to add more such commands to straighten out the permissions in /usr/local.
3. This script should run with a minimum of user interaction, but it does need the occasional 'ok' or password entry. Those could be automated, but I'm not sure it's worth it.