Fluent-ffmpeg spawn process called twice if pipe() used

[luigixx73]

Please check out this code in /base/transcoder.ts.
Lines 105 --
As using pipe() involves run() it is called twice spawning the process twice and producing 2 output streams which mess the resulting video in gliches.
So, a good solution is to put that part of code inside the else { } block when there is no custom output function.

this._promise = new Promise((resolve) => {
this._command.on('end', resolve).run();
});

[kldzj]

Hey there, thanks for spotting this issue.

Would you mind creating a PR for this?