Update segment_template.js

lib/dash/segment_template.js

@@ -103,12 +103,23 @@ shaka.dash.SegmentTemplate = class {
           context.periodInfo.start + context.periodInfo.duration : Infinity;
       const isLastPeriod = context.periodInfo.isLastPeriod;
 
-      // Don't fit live content, since it might receive more segments.
-      // Unless that live content is multi-period; it's safe to fit every period
-      // but the last one, since only the last period might receive new
-      // segments.
-      const shouldFit =
-          periodEnd != Infinity && (!isLastPeriod || !context.dynamic);
+      /* When to fit segments.  All refactors should honor/update this table:
+       *
+       * | dynamic | infinite | last   | should | notes                     |
+       * |         | period   | period | fit    |                           |
+       * | ------- | -------- | ------ | ------ | ------------------------- |
+       * |     F   |     F    |    X   |    T   | typical VOD               |
+       * |     F   |     T    |    X   |    X   | impossible: infinite VOD  |
+       * |     T   |     F    |    F   |    T   | typical live, old period  |
+       * |     T   |     F    |    T   |    F   | typical IPR               |
+       * |     T   |     T    |    F   |    X   | impossible: old, infinite |
+       * |     T   |     T    |    T   |    F   | typical live, new period  |
+       */
+
+      // We never fit the final period of dynamic content, which could be
+      // infinite live (with no limit to fit to) or IPR (which would expand the
+      // most recent segment to the end of the presentation).
+      const shouldFit = !(context.dynamic && context.periodInfo.isLastPeriod);
 
       if (segmentIndex) {
         if (shouldFit) {