youtube-dl in automator action file; video and audio not muxed
I did some more digging and found I needed to add the location of ffmpeg binary in the "do shell script" call by adding: --ffmpeg-location /usr/local/bin/ffmpeg

on run {input, parameters}
    try
        tell application "System Events"
            set pid to do shell script "cd /tmp/; /usr/local/bin/youtube-dl  --newline --ffmpeg-location /usr/local/bin/ffmpeg " &amp; input &amp; " &gt; /tmp/vidstatus 2&gt;&amp;1 &amp; echo $!"
            delay 1
            repeat while ((do shell script "kill -0 " &amp; pid) is "") -- check if pid is still responding
                display dialog "Status: " &amp; (do shell script "tail -n 1 /tmp/vidstatus") -- display last line of output
                delay 5
            end repeat
        end tell
    on error
        display notification "YouTube Download Finished" -- show error message
    end try
end run