feat: support spawn options for ffmpeg as per fluent-ffmpeg#1073

Author: vectronic

lib/processor.js

@@ -431,15 +431,17 @@ module.exports = function(proto) {
         return emitEnd(err);
       }
 
+      const options = Object.assign({
+        captureStdout: !outputStream,
+        niceness: self.options.niceness,
+        cwd: self.options.cwd,
+        windowsHide: true
+      }, self.options.processOptions || {});
+
       // Run ffmpeg
       self._spawnFfmpeg(
         args,
-        {
-          captureStdout: !outputStream,
-          niceness: self.options.niceness,
-          cwd: self.options.cwd,
-          windowsHide: true
-        }, 
+        options, 
 
         function processCB(ffmpegProc, stdoutRing, stderrRing) {
           self.ffmpegProc = ffmpegProc;
@@ -640,6 +642,20 @@ module.exports = function(proto) {
     return this;
   };
 
+  /**
+   * Add process options to spawn
+   *
+   * @method FfmpegCommand#withProcessOptions
+   * @category Processing
+   *
+   * @see [child_process.spawn](https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options)
+   * @return FfmpegCommand
+   */
+  proto.withProcessOptions = function(options) {
+    options = options || {};
+    this.options.processOptions = options;
+    return this;
+  };
 
   /**
    * Kill current ffmpeg process, if any