handle multiple caption files

app/components/embed/media_tag_component.rb

@@ -87,7 +87,27 @@ def enabled_streaming_sources
     def transcript
       return unless render_captions?
 
-      tag.track(src: file.vtt.file_url, kind: 'captions', srclang: 'en', label: 'English')
+      # A video clip may have multiple caption files in different languages.
+      # We want to enable the user to select from any of these options.
+      # We also want the different language options to be listed alphabetically.
+      safe_join(
+        file.vtt.sort_by { |cfile| caption_language(cfile.language) }.map do |caption_file|
+          lang_code = caption_file.language || 'en'
+          lang_label = caption_language(lang_code)
+          tag.track(src: caption_file.file_url, kind: 'captions', srclang: lang_code, label: lang_label)
+        end
+      )
+    end
+
+    def caption_language(language_code)
+      case language_code
+      when 'en'
+        'English'
+      when 'ru'
+        'Russian'
+      else
+        'Caption'
+      end
     end
 
     def render_captions?

app/models/embed/purl/resource.rb

@@ -55,9 +55,9 @@ def thumbnail
         files.find(&:thumbnail?)
       end
 
-      # @return [ResourceFile]
+      # @return [Array<ResourceFile>]
       def vtt
-        files.find(&:vtt?)
+        files.select(&:vtt?)
       end
     end
   end

app/models/embed/purl/resource_file.rb

@@ -62,14 +62,20 @@ def thumbnail?
         Settings.resource_types_that_contain_thumbnails.include?(resource.type)
       end
 
+      # Returns array of VTT files
       def vtt
-        resource.files.find(&:vtt?)
+        resource.files.select(&:vtt?)
       end
 
       def vtt?
         mimetype == 'text/vtt'
       end
 
+      # Returns language if specified by language tag
+      def language
+        @file.attributes['language'].try(:value)
+      end
+
       def pdf?
         mimetype == 'application/pdf'
       end

spec/components/embed/media_tag_component_spec.rb

@@ -234,4 +234,14 @@
       expect(page).to have_css('track[src="https://stacks.stanford.edu/file/druid:bc123df4567/abc_123_cap.webvtt"]')
     end
   end
+
+  context 'with multiple captions with different languages' do
+    let(:purl) { video_purl_with_multiple_vtt }
+    let(:include_transcripts) { true }
+
+    it 'has track elements with multiple languages' do
+      expect(page).to have_css('track[srclang="en"][label="English"]')
+      expect(page).to have_css('track[srclang="ru"][label="Russian"]')
+    end
+  end
 end

spec/fixtures/purl_fixtures.rb

@@ -989,6 +989,33 @@ def video_purl_with_vtt
     XML
   end
 
+  def video_purl_with_multiple_vtt
+    <<-XML
+      <publicObject>
+        <identityMetadata>
+          <objectLabel>Title of the single video</objectLabel>
+        </identityMetadata>
+        <contentMetadata type="media">
+          <resource sequence="1" id="abc123_1" type="video">
+            <file id="abc_123.mp4" mimetype="video/mp4" size="152000000"></file>
+            <file id="english_caption.webvtt" mimetype="text/vtt" size="176218" role="caption" language="en"></file>
+            <file id="russian_caption.webvtt" mimetype="text/vtt" size="176218" role="caption" language="ru"></file>
+          </resource>
+        </contentMetadata>
+        <rightsMetadata>
+          <access type="read">
+            <machine>
+              <location>spec</location>
+            </machine>
+          </access>
+        </rightsMetadata>
+        <oai_dc:dc xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:dc="http://purl.org/dc/elements/1.1/">
+          <dc:title>title of video with vtt</dc:title>
+        </oai_dc>
+      </publicObject>
+    XML
+  end
+
   def video_purl
     <<-XML
       <publicObject>

spec/models/embed/purl/resource_spec.rb

@@ -54,15 +54,15 @@
     let(:resource) { Embed::Purl.new('12345').contents.first }
 
     context 'when it has a vtt transcript' do
-      subject { resource.vtt.title }
+      subject { resource.vtt[0].title }
 
       before { stub_purl_response_with_fixture(video_purl_with_vtt) }
 
       it { is_expected.to eq 'abc_123_cap.webvtt' }
     end
 
     context 'when it does not have a vtt transcript' do
-      subject { resource.vtt }
+      subject { resource.vtt[0] }
 
       before { stub_purl_response_with_fixture(single_video_purl) }