[HLS] Support audio only master playlist

Generate an audio only master playlist if there are no videos and
subtitles.

We do not support mixing audio only EXT-X-STREAM-INF with video
EXT-X-STREAM-INF right now.

Fixes #461.

Change-Id: I999b335ad7abbe183ffcb0f5d471948977c2772f

packager/app/test/testdata/avc-ts-live-playlist-dash-dynamic-with-segment-deletion/output.m3u8

@@ -2,3 +2,6 @@
 ## Generated with https://github.com/google/shaka-packager version <tag>-<hash>-<test>
 
 #EXT-X-MEDIA:TYPE=AUDIO,URI="bear-640x360-audio.m3u8",GROUP-ID="default-audio-group",NAME="stream_0",AUTOSELECT=YES,CHANNELS="2"
+
+#EXT-X-STREAM-INF:BANDWIDTH=133850,AVERAGE-BANDWIDTH=126393,CODECS="mp4a.40.2",AUDIO="default-audio-group"
+bear-640x360-audio.m3u8

packager/app/test/testdata/flac-with-encryption/output.m3u8

@@ -2,3 +2,6 @@
 ## Generated with https://github.com/google/shaka-packager version <tag>-<hash>-<test>
 
 #EXT-X-MEDIA:TYPE=AUDIO,URI="stream_0.m3u8",GROUP-ID="default-audio-group",NAME="stream_0",AUTOSELECT=YES,CHANNELS="2"
+
+#EXT-X-STREAM-INF:BANDWIDTH=672924,AVERAGE-BANDWIDTH=631380,CODECS="flac",AUDIO="default-audio-group"
+stream_0.m3u8

packager/hls/base/master_playlist.cc

@@ -192,6 +192,7 @@ void BuildStreamInfTag(const MediaPlaylist& playlist,
 
   std::string tag_name;
   switch (playlist.stream_type()) {
+    case MediaPlaylist::MediaPlaylistStreamType::kAudio:
     case MediaPlaylist::MediaPlaylistStreamType::kVideo:
       tag_name = "#EXT-X-STREAM-INF";
       break;
@@ -219,8 +220,9 @@ void BuildStreamInfTag(const MediaPlaylist& playlist,
 
   uint32_t width;
   uint32_t height;
-  CHECK(playlist.GetDisplayResolution(&width, &height));
-  tag.AddNumberPair("RESOLUTION", width, 'x', height);
+  if (playlist.GetDisplayResolution(&width, &height)) {
+    tag.AddNumberPair("RESOLUTION", width, 'x', height);
+  }
 
   if (variant.audio_group_id) {
     tag.AddQuotedString("AUDIO", *variant.audio_group_id);
@@ -403,6 +405,23 @@ void AppendPlaylists(const std::string& default_audio_language,
       BuildStreamInfTag(*playlist, Variant(), base_url, content);
     }
   }
+
+  // Generate audio-only master playlist when there are no videos and subtitles.
+  if (!audio_playlist_groups.empty() && video_playlists.empty() &&
+      subtitle_playlist_groups.empty()) {
+    content->append("\n");
+    for (const auto& playlist_group : audio_playlist_groups) {
+      Variant variant;
+      // Populate |audio_group_id|, which will be propagated to "AUDIO" field.
+      // Leaving other fields, e.g. xxx_audio_bitrate in |Variant|, as
+      // null/empty/zero intentionally as the information is already available
+      // in audio |playlist|.
+      variant.audio_group_id = &playlist_group.first;
+      for (const auto& playlist : playlist_group.second) {
+        BuildStreamInfTag(*playlist, variant, base_url, content);
+      }
+    }
+  }
 }
 
 }  // namespace

packager/hls/base/master_playlist_unittest.cc

@@ -98,7 +98,8 @@ std::unique_ptr<MockMediaPlaylist> CreateAudioPlaylist(
   EXPECT_CALL(*playlist, AvgBitrate())
       .Times(AtLeast(1))
       .WillRepeatedly(Return(avg_bitrate));
-  EXPECT_CALL(*playlist, GetDisplayResolution(NotNull(), NotNull())).Times(0);
+  ON_CALL(*playlist, GetDisplayResolution(NotNull(), NotNull()))
+      .WillByDefault(Return(false));
 
   return playlist;
 }
@@ -640,5 +641,56 @@ TEST_F(MasterPlaylistTest, WriteMasterPlaylistMixedPlaylistsDifferentGroups) {
 
   ASSERT_EQ(expected, actual);
 }
+
+TEST_F(MasterPlaylistTest, WriteMasterPlaylistAudioOnly) {
+  const uint64_t kAudioChannels = 2;
+  const uint64_t kAudioMaxBitrate = 50000;
+  const uint64_t kAudioAvgBitrate = 30000;
+
+  std::unique_ptr<MockMediaPlaylist> media_playlists[] = {
+      // AUDIO
+      CreateAudioPlaylist("audio-1.m3u8", "audio 1", "audio-group-1",
+                          "audiocodec", "en", kAudioChannels, kAudioMaxBitrate,
+                          kAudioAvgBitrate),
+      CreateAudioPlaylist("audio-2.m3u8", "audio 2", "audio-group-2",
+                          "audiocodec", "fr", kAudioChannels, kAudioMaxBitrate,
+                          kAudioAvgBitrate),
+  };
+
+  // Add all the media playlists to the master playlist.
+  std::list<MediaPlaylist*> media_playlist_list;
+  for (const auto& media_playlist : media_playlists) {
+    media_playlist_list.push_back(media_playlist.get());
+  }
+
+  const char kBaseUrl[] = "http://playlists.org/";
+  EXPECT_TRUE(master_playlist_.WriteMasterPlaylist(kBaseUrl, test_output_dir_,
+                                                   media_playlist_list));
+
+  std::string actual;
+  ASSERT_TRUE(File::ReadFileToString(master_playlist_path_.c_str(), &actual));
+
+  const std::string expected =
+      "#EXTM3U\n"
+      "## Generated with https://github.com/google/shaka-packager version "
+      "test\n"
+      "\n"
+      "#EXT-X-MEDIA:TYPE=AUDIO,URI=\"http://playlists.org/audio-1.m3u8\","
+      "GROUP-ID=\"audio-group-1\",LANGUAGE=\"en\",NAME=\"audio 1\","
+      "DEFAULT=YES,AUTOSELECT=YES,CHANNELS=\"2\"\n"
+      "#EXT-X-MEDIA:TYPE=AUDIO,URI=\"http://playlists.org/audio-2.m3u8\","
+      "GROUP-ID=\"audio-group-2\",LANGUAGE=\"fr\",NAME=\"audio 2\","
+      "AUTOSELECT=YES,CHANNELS=\"2\"\n"
+      "\n"
+      "#EXT-X-STREAM-INF:BANDWIDTH=50000,AVERAGE-BANDWIDTH=30000,"
+      "CODECS=\"audiocodec\",AUDIO=\"audio-group-1\"\n"
+      "http://playlists.org/audio-1.m3u8\n"
+      "#EXT-X-STREAM-INF:BANDWIDTH=50000,AVERAGE-BANDWIDTH=30000,"
+      "CODECS=\"audiocodec\",AUDIO=\"audio-group-2\"\n"
+      "http://playlists.org/audio-2.m3u8\n";
+
+  ASSERT_EQ(expected, actual);
+}
+
 }  // namespace hls
 }  // namespace shaka