Call system package with Go on App Engine Standard - google-app-engine

Question

I'm trying to use FFmpeg in a Go application thats running on Google App Engine Standard. I can get this to run locally, when I point to a local instance of the FFmpeg binary using exec.Command()
cmd := exec.Command(
"/Users/justin/Desktop/conversion/ffmpeg", // this won't work on a remote server
"-i", "pipe:0",
"-ac", "1",
"-codec:a", "libmp3lame",
"-b:a", "48k",
"-ar", "24000",
"-f", "mp3",
"pipe:1",
)
cmd.Stdin = bytes.NewReader(synthResp.AudioContent)
var output bytes.Buffer
cmd.Stdout = &output
err = cmd.Run()
Obviously, this won't work when I deploy the application, so I need a way to point to a hosted version of the FFmpeg binary. It seems ffmpeg is a system package for the go1.11 App Engine Standard environment.
What are "System packages" and how do I use them?
When I look for documentation, I find a lot of documentation on apt-get, and no documentation on how to use them, App Engine or otherwise. Do I need to install it, or should it already be part of the container(?) that App Engine is running?
Do I call it, like I'd call other executables? If so, that I'd expect this to work, but it doesn't
cmd := exec.Command(
"ffmpeg", // <------ what should this be?
"-i", "pipe:0",
"-ac", "1",
"-codec:a", "libmp3lame",
"-b:a", "48k",
"-ar", "24000",
"-f", "mp3",
"pipe:1",
)
cmd.Stdin = bytes.NewReader(synthResp.AudioContent)
var output bytes.Buffer
cmd.Stdout = &output
err = cmd.Run()
Logging err, I see exec: "ffmpeg": executable file not found in $PATH

Answer 1

Thanks to question asked by #iLoveReflection I realize that the locally running version of the app will call the ffmpeg command, expecting it to be in a location pointed to by the standard $PATH environmental variable. I had thought App Engine would recognize the call to ffmpeg and use an executable it had installed in a custom location.
Moving the ffmpeg executable to /usr/local/bin, and ensuring $PATH included that directory fixed the issue.