Look I want to know the filesize of the output file that will be downloaded into my system even before its downloaded

I'm trimming some random url files and downloading them But I want to know how much gb,mb,kb, I need to download even before the download is completed.

I'm using ffmpeg in node js so It doesn't actually shows me anything other then when the process is done,

My code

exec(`ffmpeg -ss ${start} -to ${end} -i "${url}" -c copy -avoid_negative_ts make_zero "${filename}"`, (error, stdout, stderr) => {
if (error) {
        return;
      } else {
        res.send({ "url": filename });
      }
 })

Please tell me a solution how can I know how much is the output filesize that needs to be downloaded intotal so that I can tell the user that this is the total trimmed filesize while he would be waiting till the file will be downloaded on my server then I'll let user download the file from my server to his pc or mobile :)

Help :)