Add support for variable substition in HLS

Issue:#4422

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=209958623

RELEASENOTES.md

@@ -70,6 +70,8 @@
   * Allow configuration of the Loader retry delay
     ([#3370](https://github.com/google/ExoPlayer/issues/3370)).
 * HLS:
+  * Add support for variable substitution
+    ([#4422](https://github.com/google/ExoPlayer/issues/4422)).
   * Add support for PlayReady.
   * Add support for alternative EXT-X-KEY tags.
   * Set the bitrate on primary track sample formats

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/playlist/HlsMasterPlaylist.java

@@ -21,6 +21,7 @@ import com.google.android.exoplayer2.util.MimeTypes;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
 /** Represents an HLS master playlist. */
 public final class HlsMasterPlaylist extends HlsPlaylist {
@@ -35,7 +36,8 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
           /* subtitles= */ Collections.emptyList(),
           /* muxedAudioFormat= */ null,
           /* muxedCaptionFormats= */ Collections.emptyList(),
-          /* hasIndependentSegments= */ false);
+          /* hasIndependentSegments= */ false,
+          /* variableDefinitions= */ Collections.emptyMap());
 
   public static final int GROUP_INDEX_VARIANT = 0;
   public static final int GROUP_INDEX_AUDIO = 1;
@@ -110,6 +112,8 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
    * captions information.
    */
   public final List<Format> muxedCaptionFormats;
+  /** Contains variable definitions, as defined by the #EXT-X-DEFINE tag. */
+  public final Map<String, String> variableDefinitions;
 
   /**
    * @param baseUri See {@link #baseUri}.
@@ -120,6 +124,7 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
    * @param muxedAudioFormat See {@link #muxedAudioFormat}.
    * @param muxedCaptionFormats See {@link #muxedCaptionFormats}.
    * @param hasIndependentSegments See {@link #hasIndependentSegments}.
+   * @param variableDefinitions See {@link #variableDefinitions}.
    */
   public HlsMasterPlaylist(
       String baseUri,
@@ -129,7 +134,8 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
       List<HlsUrl> subtitles,
       Format muxedAudioFormat,
       List<Format> muxedCaptionFormats,
-      boolean hasIndependentSegments) {
+      boolean hasIndependentSegments,
+      Map<String, String> variableDefinitions) {
     super(baseUri, tags, hasIndependentSegments);
     this.variants = Collections.unmodifiableList(variants);
     this.audios = Collections.unmodifiableList(audios);
@@ -137,6 +143,7 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
     this.muxedAudioFormat = muxedAudioFormat;
     this.muxedCaptionFormats = muxedCaptionFormats != null
         ? Collections.unmodifiableList(muxedCaptionFormats) : null;
+    this.variableDefinitions = Collections.unmodifiableMap(variableDefinitions);
   }
 
   @Override
@@ -149,7 +156,8 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
         copyRenditionsList(subtitles, GROUP_INDEX_SUBTITLE, streamKeys),
         muxedAudioFormat,
         muxedCaptionFormats,
-        hasIndependentSegments);
+        hasIndependentSegments,
+        variableDefinitions);
   }
 
   /**
@@ -169,7 +177,8 @@ public final class HlsMasterPlaylist extends HlsPlaylist {
         emptyList,
         /* muxedAudioFormat= */ null,
         /* muxedCaptionFormats= */ null,
-        /* hasIndependentSegments= */ false);
+        /* hasIndependentSegments= */ false,
+        /* variableDefinitions= */ Collections.emptyMap());
   }
 
   private static List<HlsUrl> copyRenditionsList(

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/playlist/HlsPlaylistParser.java

@@ -40,6 +40,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Queue;
 import java.util.TreeMap;
 import java.util.regex.Matcher;
@@ -57,6 +58,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
 
   private static final String TAG_VERSION = "#EXT-X-VERSION";
   private static final String TAG_PLAYLIST_TYPE = "#EXT-X-PLAYLIST-TYPE";
+  private static final String TAG_DEFINE = "#EXT-X-DEFINE";
   private static final String TAG_STREAM_INF = "#EXT-X-STREAM-INF";
   private static final String TAG_MEDIA = "#EXT-X-MEDIA";
   private static final String TAG_TARGET_DURATION = "#EXT-X-TARGETDURATION";
@@ -147,6 +149,10 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
   private static final Pattern REGEX_AUTOSELECT = compileBooleanAttrPattern("AUTOSELECT");
   private static final Pattern REGEX_DEFAULT = compileBooleanAttrPattern("DEFAULT");
   private static final Pattern REGEX_FORCED = compileBooleanAttrPattern("FORCED");
+  private static final Pattern REGEX_VALUE = Pattern.compile("VALUE=\"(.+?)\"");
+  private static final Pattern REGEX_IMPORT = Pattern.compile("IMPORT=\"(.+?)\"");
+  private static final Pattern REGEX_VARIABLE_REFERENCE =
+      Pattern.compile("\\{\\$([a-zA-Z0-9\\-_]+)\\}");
 
   private final HlsMasterPlaylist masterPlaylist;
 
@@ -239,6 +245,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
       throws IOException {
     HashSet<String> variantUrls = new HashSet<>();
     HashMap<String, String> audioGroupIdToCodecs = new HashMap<>();
+    HashMap<String, String> variableDefinitions = new HashMap<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> variants = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> audios = new ArrayList<>();
     ArrayList<HlsMasterPlaylist.HlsUrl> subtitles = new ArrayList<>();
@@ -258,7 +265,11 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
         tags.add(line);
       }
 
-      if (line.equals(TAG_INDEPENDENT_SEGMENTS)) {
+      if (line.startsWith(TAG_DEFINE)) {
+        variableDefinitions.put(
+            /* key= */ parseStringAttr(line, REGEX_NAME, variableDefinitions),
+            /* value= */ parseStringAttr(line, REGEX_VALUE, variableDefinitions));
+      } else if (line.equals(TAG_INDEPENDENT_SEGMENTS)) {
         hasIndependentSegmentsTag = true;
       } else if (line.startsWith(TAG_MEDIA)) {
         // Media tags are parsed at the end to include codec information from #EXT-X-STREAM-INF
@@ -267,13 +278,15 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
       } else if (line.startsWith(TAG_STREAM_INF)) {
         noClosedCaptions |= line.contains(ATTR_CLOSED_CAPTIONS_NONE);
         int bitrate = parseIntAttr(line, REGEX_BANDWIDTH);
-        String averageBandwidthString = parseOptionalStringAttr(line, REGEX_AVERAGE_BANDWIDTH);
+        String averageBandwidthString =
+            parseOptionalStringAttr(line, REGEX_AVERAGE_BANDWIDTH, variableDefinitions);
         if (averageBandwidthString != null) {
           // If available, the average bandwidth attribute is used as the variant's bitrate.
           bitrate = Integer.parseInt(averageBandwidthString);
         }
-        String codecs = parseOptionalStringAttr(line, REGEX_CODECS);
+        String codecs = parseOptionalStringAttr(line, REGEX_CODECS, variableDefinitions);
-        String resolutionString = parseOptionalStringAttr(line, REGEX_RESOLUTION);
+        String resolutionString =
+            parseOptionalStringAttr(line, REGEX_RESOLUTION, variableDefinitions);
         int width;
         int height;
         if (resolutionString != null) {
@@ -290,15 +303,18 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
           height = Format.NO_VALUE;
         }
         float frameRate = Format.NO_VALUE;
-        String frameRateString = parseOptionalStringAttr(line, REGEX_FRAME_RATE);
+        String frameRateString =
+            parseOptionalStringAttr(line, REGEX_FRAME_RATE, variableDefinitions);
         if (frameRateString != null) {
           frameRate = Float.parseFloat(frameRateString);
         }
-        String audioGroupId = parseOptionalStringAttr(line, REGEX_AUDIO);
+        String audioGroupId = parseOptionalStringAttr(line, REGEX_AUDIO, variableDefinitions);
         if (audioGroupId != null && codecs != null) {
           audioGroupIdToCodecs.put(audioGroupId, Util.getCodecsOfType(codecs, C.TRACK_TYPE_AUDIO));
         }
-        line = iterator.next(); // #EXT-X-STREAM-INF's URI.
+        line =
+            replaceVariableReferences(
+                iterator.next(), variableDefinitions); // #EXT-X-STREAM-INF's URI.
         if (variantUrls.add(line)) {
           Format format =
               Format.createVideoContainerFormat(
@@ -321,12 +337,12 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     for (int i = 0; i < mediaTags.size(); i++) {
       line = mediaTags.get(i);
       @C.SelectionFlags int selectionFlags = parseSelectionFlags(line);
-      String uri = parseOptionalStringAttr(line, REGEX_URI);
+      String uri = parseOptionalStringAttr(line, REGEX_URI, variableDefinitions);
-      String name = parseStringAttr(line, REGEX_NAME);
+      String name = parseStringAttr(line, REGEX_NAME, variableDefinitions);
-      String language = parseOptionalStringAttr(line, REGEX_LANGUAGE);
+      String language = parseOptionalStringAttr(line, REGEX_LANGUAGE, variableDefinitions);
-      String groupId = parseOptionalStringAttr(line, REGEX_GROUP_ID);
+      String groupId = parseOptionalStringAttr(line, REGEX_GROUP_ID, variableDefinitions);
       Format format;
-      switch (parseStringAttr(line, REGEX_TYPE)) {
+      switch (parseStringAttr(line, REGEX_TYPE, variableDefinitions)) {
         case TYPE_AUDIO:
           String codecs = audioGroupIdToCodecs.get(groupId);
           String sampleMimeType = codecs != null ? MimeTypes.getMediaMimeType(codecs) : null;
@@ -363,7 +379,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
           subtitles.add(new HlsMasterPlaylist.HlsUrl(uri, format));
           break;
         case TYPE_CLOSED_CAPTIONS:
-          String instreamId = parseStringAttr(line, REGEX_INSTREAM_ID);
+          String instreamId = parseStringAttr(line, REGEX_INSTREAM_ID, variableDefinitions);
           String mimeType;
           int accessibilityChannel;
           if (instreamId.startsWith("CC")) {
@@ -405,7 +421,8 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
         subtitles,
         muxedAudioFormat,
         muxedCaptionFormats,
-        hasIndependentSegmentsTag);
+        hasIndependentSegmentsTag,
+        variableDefinitions);
   }
 
   @C.SelectionFlags
@@ -433,6 +450,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     boolean hasIndependentSegmentsTag = masterPlaylist.hasIndependentSegments;
     boolean hasEndTag = false;
     Segment initializationSegment = null;
+    HashMap<String, String> variableDefinitions = new HashMap<>();
     List<Segment> segments = new ArrayList<>();
     List<String> tags = new ArrayList<>();
 
@@ -465,7 +483,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
       }
 
       if (line.startsWith(TAG_PLAYLIST_TYPE)) {
-        String playlistTypeString = parseStringAttr(line, REGEX_PLAYLIST_TYPE);
+        String playlistTypeString = parseStringAttr(line, REGEX_PLAYLIST_TYPE, variableDefinitions);
         if ("VOD".equals(playlistTypeString)) {
           playlistType = HlsMediaPlaylist.PLAYLIST_TYPE_VOD;
         } else if ("EVENT".equals(playlistTypeString)) {
@@ -474,8 +492,8 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
       } else if (line.startsWith(TAG_START)) {
         startOffsetUs = (long) (parseDoubleAttr(line, REGEX_TIME_OFFSET) * C.MICROS_PER_SECOND);
       } else if (line.startsWith(TAG_INIT_SEGMENT)) {
-        String uri = parseStringAttr(line, REGEX_URI);
+        String uri = parseStringAttr(line, REGEX_URI, variableDefinitions);
-        String byteRange = parseOptionalStringAttr(line, REGEX_ATTR_BYTERANGE);
+        String byteRange = parseOptionalStringAttr(line, REGEX_ATTR_BYTERANGE, variableDefinitions);
         if (byteRange != null) {
           String[] splitByteRange = byteRange.split("@");
           segmentByteRangeLength = Long.parseLong(splitByteRange[0]);
@@ -493,24 +511,39 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
         segmentMediaSequence = mediaSequence;
       } else if (line.startsWith(TAG_VERSION)) {
         version = parseIntAttr(line, REGEX_VERSION);
+      } else if (line.startsWith(TAG_DEFINE)) {
+        String importName = parseOptionalStringAttr(line, REGEX_IMPORT, variableDefinitions);
+        if (importName != null) {
+          String value = masterPlaylist.variableDefinitions.get(importName);
+          if (value != null) {
+            variableDefinitions.put(importName, value);
+          } else {
+            // The master playlist does not declare the imported variable. Ignore.
+          }
+        } else {
+          variableDefinitions.put(
+              parseStringAttr(line, REGEX_NAME, variableDefinitions),
+              parseStringAttr(line, REGEX_VALUE, variableDefinitions));
+        }
       } else if (line.startsWith(TAG_MEDIA_DURATION)) {
         segmentDurationUs =
             (long) (parseDoubleAttr(line, REGEX_MEDIA_DURATION) * C.MICROS_PER_SECOND);
-        segmentTitle = parseOptionalStringAttr(line, REGEX_MEDIA_TITLE, "");
+        segmentTitle = parseOptionalStringAttr(line, REGEX_MEDIA_TITLE, "", variableDefinitions);
       } else if (line.startsWith(TAG_KEY)) {
-        String method = parseStringAttr(line, REGEX_METHOD);
+        String method = parseStringAttr(line, REGEX_METHOD, variableDefinitions);
-        String keyFormat = parseOptionalStringAttr(line, REGEX_KEYFORMAT, KEYFORMAT_IDENTITY);
+        String keyFormat =
+            parseOptionalStringAttr(line, REGEX_KEYFORMAT, KEYFORMAT_IDENTITY, variableDefinitions);
         encryptionKeyUri = null;
         encryptionIV = null;
         if (METHOD_NONE.equals(method)) {
           currentSchemeDatas.clear();
           cachedDrmInitData = null;
         } else /* !METHOD_NONE.equals(method) */ {
-          encryptionIV = parseOptionalStringAttr(line, REGEX_IV);
+          encryptionIV = parseOptionalStringAttr(line, REGEX_IV, variableDefinitions);
           if (KEYFORMAT_IDENTITY.equals(keyFormat)) {
             if (METHOD_AES_128.equals(method)) {
               // The segment is fully encrypted using an identity key.
-              encryptionKeyUri = parseStringAttr(line, REGEX_URI);
+              encryptionKeyUri = parseStringAttr(line, REGEX_URI, variableDefinitions);
             } else {
               // Do nothing. Samples are encrypted using an identity key, but this is not supported.
               // Hopefully, a traditional DRM alternative is also provided.
@@ -524,9 +557,9 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
             }
             SchemeData schemeData;
             if (KEYFORMAT_PLAYREADY.equals(keyFormat)) {
-              schemeData = parsePlayReadySchemeData(line);
+              schemeData = parsePlayReadySchemeData(line, variableDefinitions);
             } else {
-              schemeData = parseWidevineSchemeData(line, keyFormat);
+              schemeData = parseWidevineSchemeData(line, keyFormat, variableDefinitions);
             }
             if (schemeData != null) {
               cachedDrmInitData = null;
@@ -535,7 +568,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
           }
         }
       } else if (line.startsWith(TAG_BYTERANGE)) {
-        String byteRange = parseStringAttr(line, REGEX_BYTERANGE);
+        String byteRange = parseStringAttr(line, REGEX_BYTERANGE, variableDefinitions);
         String[] splitByteRange = byteRange.split("@");
         segmentByteRangeLength = Long.parseLong(splitByteRange[0]);
         if (splitByteRange.length > 1) {
@@ -587,7 +620,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
 
         segments.add(
             new Segment(
-                line,
+                replaceVariableReferences(line, variableDefinitions),
                 initializationSegment,
                 segmentTitle,
                 segmentDurationUs,
@@ -627,24 +660,29 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
         segments);
   }
 
-  private static @Nullable SchemeData parsePlayReadySchemeData(String line) throws ParserException {
+  private static @Nullable SchemeData parsePlayReadySchemeData(
-    String keyFormatVersions = parseOptionalStringAttr(line, REGEX_KEYFORMATVERSIONS, "1");
+      String line, Map<String, String> variableDefinitions) throws ParserException {
+    String keyFormatVersions =
+        parseOptionalStringAttr(line, REGEX_KEYFORMATVERSIONS, "1", variableDefinitions);
     if (!"1".equals(keyFormatVersions)) {
       // Not supported.
       return null;
     }
-    String uriString = parseStringAttr(line, REGEX_URI);
+    String uriString = parseStringAttr(line, REGEX_URI, variableDefinitions);
     byte[] data = Base64.decode(uriString.substring(uriString.indexOf(',')), Base64.DEFAULT);
     byte[] psshData = PsshAtomUtil.buildPsshAtom(C.PLAYREADY_UUID, data);
     return new SchemeData(C.PLAYREADY_UUID, MimeTypes.VIDEO_MP4, psshData);
   }
 
-  private static @Nullable SchemeData parseWidevineSchemeData(String line, String keyFormat)
+  private static @Nullable SchemeData parseWidevineSchemeData(
+      String line, String keyFormat, Map<String, String> variableDefinitions)
       throws ParserException {
     if (KEYFORMAT_WIDEVINE_PSSH_BINARY.equals(keyFormat)) {
-     String uriString = parseStringAttr(line, REGEX_URI);
+      String uriString = parseStringAttr(line, REGEX_URI, variableDefinitions);
-     return new SchemeData(C.WIDEVINE_UUID, MimeTypes.VIDEO_MP4,
+      return new SchemeData(
-         Base64.decode(uriString.substring(uriString.indexOf(',')), Base64.DEFAULT));
+          C.WIDEVINE_UUID,
+          MimeTypes.VIDEO_MP4,
+          Base64.decode(uriString.substring(uriString.indexOf(',')), Base64.DEFAULT));
     }
     if (KEYFORMAT_WIDEVINE_PSSH_JSON.equals(keyFormat)) {
       try {
@@ -657,19 +695,21 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
   }
 
   private static int parseIntAttr(String line, Pattern pattern) throws ParserException {
-    return Integer.parseInt(parseStringAttr(line, pattern));
+    return Integer.parseInt(parseStringAttr(line, pattern, Collections.emptyMap()));
   }
 
   private static long parseLongAttr(String line, Pattern pattern) throws ParserException {
-    return Long.parseLong(parseStringAttr(line, pattern));
+    return Long.parseLong(parseStringAttr(line, pattern, Collections.emptyMap()));
   }
 
   private static double parseDoubleAttr(String line, Pattern pattern) throws ParserException {
-    return Double.parseDouble(parseStringAttr(line, pattern));
+    return Double.parseDouble(parseStringAttr(line, pattern, Collections.emptyMap()));
   }
 
-  private static String parseStringAttr(String line, Pattern pattern) throws ParserException {
+  private static String parseStringAttr(
-    String value = parseOptionalStringAttr(line, pattern);
+      String line, Pattern pattern, Map<String, String> variableDefinitions)
+      throws ParserException {
+    String value = parseOptionalStringAttr(line, pattern, variableDefinitions);
     if (value != null) {
       return value;
     } else {
@@ -677,14 +717,39 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     }
   }
 
-  private static @Nullable String parseOptionalStringAttr(String line, Pattern pattern) {
+  private static @Nullable String parseOptionalStringAttr(
-    return parseOptionalStringAttr(line, pattern, null);
+      String line, Pattern pattern, Map<String, String> variableDefinitions) {
+    return parseOptionalStringAttr(line, pattern, null, variableDefinitions);
   }
 
   private static @PolyNull String parseOptionalStringAttr(
-      String line, Pattern pattern, @PolyNull String defaultValue) {
+      String line,
+      Pattern pattern,
+      @PolyNull String defaultValue,
+      Map<String, String> variableDefinitions) {
     Matcher matcher = pattern.matcher(line);
-    return matcher.find() ? matcher.group(1) : defaultValue;
+    String value = matcher.find() ? matcher.group(1) : defaultValue;
+    return variableDefinitions.isEmpty() || value == null
+        ? value
+        : replaceVariableReferences(value, variableDefinitions);
+  }
+
+  private static String replaceVariableReferences(
+      String string, Map<String, String> variableDefinitions) {
+    Matcher matcher = REGEX_VARIABLE_REFERENCE.matcher(string);
+    // TODO: Replace StringBuffer with StringBuilder once Java 9 is available.
+    StringBuffer stringWithReplacements = new StringBuffer();
+    while (matcher.find()) {
+      String groupName = matcher.group(1);
+      if (variableDefinitions.containsKey(groupName)) {
+        matcher.appendReplacement(
+            stringWithReplacements, Matcher.quoteReplacement(variableDefinitions.get(groupName)));
+      } else {
+        // The variable is not defined. The value is ignored.
+      }
+    }
+    matcher.appendTail(stringWithReplacements);
+    return stringWithReplacements.toString();
   }
 
   private static boolean parseOptionalBooleanAttribute(

library/hls/src/test/java/com/google/android/exoplayer2/source/hls/playlist/HlsMasterPlaylistParserTest.java

@@ -117,6 +117,15 @@ public class HlsMasterPlaylistParserTest {
           + "#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS=\"mp4a.40.2 , avc1.66.30 \"\n"
           + "http://example.com/spaces_in_codecs.m3u8\n";
 
+  private static final String PLAYLIST_WITH_VARIABLE_SUBSTITUTION =
+      " #EXTM3U \n"
+          + "\n"
+          + "#EXT-X-DEFINE:NAME=\"codecs\",VALUE=\"mp4a.40.5\"\n"
+          + "#EXT-X-DEFINE:NAME=\"tricky\",VALUE=\"This/{$nested}/reference/shouldnt/work\"\n"
+          + "#EXT-X-DEFINE:NAME=\"nested\",VALUE=\"This should not be inserted\"\n"
+          + "#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS=\"{$codecs}\"\n"
+          + "http://example.com/{$tricky}\n";
+
   @Test
   public void testParseMasterPlaylist() throws IOException {
     HlsMasterPlaylist masterPlaylist = parseMasterPlaylist(PLAYLIST_URI, PLAYLIST_SIMPLE);
@@ -218,6 +227,15 @@ public class HlsMasterPlaylistParserTest {
     assertThat(playlistWithoutIndependentSegments.hasIndependentSegments).isFalse();
   }
 
+  @Test
+  public void testVariableSubstitution() throws IOException {
+    HlsMasterPlaylist playlistWithSubstitutions =
+        parseMasterPlaylist(PLAYLIST_URI, PLAYLIST_WITH_VARIABLE_SUBSTITUTION);
+    HlsMasterPlaylist.HlsUrl variant = playlistWithSubstitutions.variants.get(0);
+    assertThat(variant.format.codecs).isEqualTo("mp4a.40.5");
+    assertThat(variant.url).isEqualTo("http://example.com/This/{$nested}/reference/shouldnt/work");
+  }
+
   private static HlsMasterPlaylist parseMasterPlaylist(String uri, String playlistString)
       throws IOException {
     Uri playlistUri = Uri.parse(uri);

library/hls/src/test/java/com/google/android/exoplayer2/source/hls/playlist/HlsMediaPlaylistParserTest.java

@@ -25,6 +25,7 @@ import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -397,9 +398,71 @@ public class HlsMediaPlaylistParserTest {
             /* subtitles= */ Collections.emptyList(),
             /* muxedAudioFormat= */ null,
             /* muxedCaptionFormats= */ null,
-            /* hasIndependentSegments= */ true);
+            /* hasIndependentSegments= */ true,
+            /* variableDefinitions */ Collections.emptyMap());
     HlsMediaPlaylist playlistWithInheritance =
         (HlsMediaPlaylist) new HlsPlaylistParser(masterPlaylist).parse(playlistUri, inputStream);
     assertThat(playlistWithInheritance.hasIndependentSegments).isTrue();
   }
+
+  @Test
+  public void testVariableSubstitution() throws IOException {
+    Uri playlistUri = Uri.parse("https://example.com/substitution.m3u8");
+    String playlistString =
+        "#EXTM3U\n"
+            + "#EXT-X-VERSION:8\n"
+            + "#EXT-X-DEFINE:NAME=\"underscore_1\",VALUE=\"{\"\n"
+            + "#EXT-X-DEFINE:NAME=\"dash-1\",VALUE=\"replaced_value.ts\"\n"
+            + "#EXT-X-TARGETDURATION:5\n"
+            + "#EXT-X-MEDIA-SEQUENCE:10\n"
+            + "#EXTINF:5.005,\n"
+            + "segment1.ts\n"
+            + "#EXT-X-MAP:URI=\"{$dash-1}\""
+            + "#EXTINF:5.005,\n"
+            + "segment{$underscore_1}$name_1}\n";
+    InputStream inputStream = new ByteArrayInputStream(Util.getUtf8Bytes(playlistString));
+    HlsMediaPlaylist playlist =
+        (HlsMediaPlaylist) new HlsPlaylistParser().parse(playlistUri, inputStream);
+    Segment segment = playlist.segments.get(1);
+    assertThat(segment.initializationSegment.url).isEqualTo("replaced_value.ts");
+    assertThat(segment.url).isEqualTo("segment{$name_1}");
+  }
+
+  @Test
+  public void testInheritedVariableSubstitution() throws IOException {
+    Uri playlistUri = Uri.parse("https://example.com/test3.m3u8");
+    String playlistString =
+        "#EXTM3U\n"
+            + "#EXT-X-VERSION:8\n"
+            + "#EXT-X-TARGETDURATION:5\n"
+            + "#EXT-X-MEDIA-SEQUENCE:10\n"
+            + "#EXT-X-DEFINE:IMPORT=\"imported_base\"\n"
+            + "#EXTINF:5.005,\n"
+            + "{$imported_base}1.ts\n"
+            + "#EXTINF:5.005,\n"
+            + "{$imported_base}2.ts\n"
+            + "#EXTINF:5.005,\n"
+            + "{$imported_base}3.ts\n"
+            + "#EXTINF:5.005,\n"
+            + "{$imported_base}4.ts\n";
+    InputStream inputStream = new ByteArrayInputStream(Util.getUtf8Bytes(playlistString));
+    HashMap<String, String> variableDefinitions = new HashMap<>();
+    variableDefinitions.put("imported_base", "long_path");
+    HlsMasterPlaylist masterPlaylist =
+        new HlsMasterPlaylist(
+            /* baseUri= */ "",
+            /* tags= */ Collections.emptyList(),
+            /* variants= */ Collections.emptyList(),
+            /* audios= */ Collections.emptyList(),
+            /* subtitles= */ Collections.emptyList(),
+            /* muxedAudioFormat= */ null,
+            /* muxedCaptionFormats= */ Collections.emptyList(),
+            /* hasIndependentSegments= */ false,
+            variableDefinitions);
+    HlsMediaPlaylist playlist =
+        (HlsMediaPlaylist) new HlsPlaylistParser(masterPlaylist).parse(playlistUri, inputStream);
+    for (int i = 1; i <= 4; i++) {
+      assertThat(playlist.segments.get(i - 1).url).isEqualTo("long_path" + i + ".ts");
+    }
+  }
 }