Add default_language flag

Setting this flag will tag any matching tracks with kRoleMain.
The player will then know which tracks should be default when there
is not a language match.

Closes #155

Change-Id: I827304c49e345d07b1e76f7a46421b60f228f0ba

packager/app/mpd_flags.cc

@@ -43,6 +43,11 @@ DEFINE_double(suggested_presentation_delay,
               0.0,
               "Specifies a delay, in seconds, to be added to the media "
               "presentation time. This value is used for live profile only.");
+DEFINE_string(default_language,
+              "",
+              "Any tracks tagged with this language will have "
+              "<Role ... value=\"main\" /> in the manifest.  This allows the "
+              "player to choose the correct default language for the content.");
 DEFINE_bool(generate_dash_if_iop_compliant_mpd,
             false,
             "Try to generate DASH-IF IOPv3 compliant MPD. This is best effort "

packager/app/mpd_flags.h

@@ -19,6 +19,7 @@ DECLARE_double(minimum_update_period);
 DECLARE_double(min_buffer_time);
 DECLARE_double(time_shift_buffer_depth);
 DECLARE_double(suggested_presentation_delay);
+DECLARE_string(default_language);
 DECLARE_bool(generate_dash_if_iop_compliant_mpd);
 
 #endif  // APP_MPD_FLAGS_H_

packager/app/packager_util.cc

@@ -177,6 +177,7 @@ bool GetMpdOptions(MpdOptions* mpd_options) {
   mpd_options->time_shift_buffer_depth = FLAGS_time_shift_buffer_depth;
   mpd_options->suggested_presentation_delay =
       FLAGS_suggested_presentation_delay;
+  mpd_options->default_language = FLAGS_default_language;
   return true;
 }
 

packager/mpd/base/mpd_builder.cc

@@ -413,8 +413,12 @@ AdaptationSet* MpdBuilder::AddAdaptationSet(const std::string& lang) {
   std::unique_ptr<AdaptationSet> adaptation_set(
       new AdaptationSet(adaptation_set_counter_.GetNext(), lang, mpd_options_,
                         type_, &representation_counter_));
-
   DCHECK(adaptation_set);
+
+  if (!lang.empty() && lang == mpd_options_.default_language) {
+    adaptation_set->AddRole(AdaptationSet::kRoleMain);
+  }
+
   adaptation_sets_.push_back(std::move(adaptation_set));
   return adaptation_sets_.back().get();
 }

packager/mpd/base/mpd_options.h

@@ -28,6 +28,7 @@ struct MpdOptions {
   double min_buffer_time;
   double time_shift_buffer_depth;
   double suggested_presentation_delay;
+  std::string default_language;
 };
 
 }  // namespace shaka