Make imsc settings options less generic

Author: ryanmccartney

src/core/Settings.js

@@ -513,8 +513,22 @@ import Events from './events/Events';
  * When true, only those captions where itts:forcedDisplay="true" will be displayed.
  * @property {boolean} [imsc.enableRollUp=true]
  * Enable/disable rollUp style display of IMSC captions.
- * @property {number} [imsc.options]
- * IMSC styling options - including; sizeAdjust, lineHeightAdjust, backgroundOpacityScale and fontFamily. See the renderHtml function of imscJS for full details 
+ * @property {object} [imsc.options]
+ * IMSC styling options - See the renderHtml function of imscJS for full details 
+ * @property {number} [imsc.options.sizeAdjust]
+ * IMSC styling option - scales the text size and line padding
+ * @property {number} [imsc.options.lineHeightAdjust]
+ * IMSC styling option - scales the line height
+ * @property {number} [imsc.options.backgroundOpacityScale]
+ * IMSC styling option - scales the backgroundColor opacity
+ * @property {string} [imsc.options.fontFamily]
+ * IMSC styling option - comma-separated list of font family values to use, if present.
+ * @property {number} [imsc.options.colorOpacityScale]
+ * IMSC styling option - opacity override on text color
+ * @property {number} [imsc.options.regionOpacityScale]
+ * IMSC styling option - scales the region opacity
+ * @property {string} [imsc.options.textOutline]
+ * IMSC styling option - textOutline value to use, if present
  * @property {object} [webvtt.customRenderingEnabled=false]
  * Enables the custom rendering for WebVTT captions. For details refer to the "Subtitles and Captions" sample section of dash.js.
  * Custom WebVTT rendering requires the external library vtt.js that can be found in the contrib folder.
@@ -1011,7 +1025,15 @@ function Settings() {
                 imsc: {
                     displayForcedOnlyMode: false,
                     enableRollUp: true,
-                    options: {},
+                    options: {
+                        sizeAdjust: 1,
+                        lineHeightAdjust: 1,
+                        backgroundOpacityScale: null,
+                        fontFamily: null,
+                        colorOpacityScale: 1,
+                        regionOpacityScale: null,
+                        textOutline: null,
+                    },
                 },
                 webvtt: {
                     customRenderingEnabled: false