Define the SubtitleParser interface

We will migrate concrete implementations of `SubtitleDecoder` to implement
this instead.

PiperOrigin-RevId: 537298600

libraries/extractor/src/main/java/androidx/media3/extractor/text/SubtitleParser.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.media3.extractor.text;
+
+import androidx.annotation.Nullable;
+import androidx.media3.common.text.CueGroup;
+import androidx.media3.common.util.UnstableApi;
+import java.util.List;
+
+/**
+ * Parses subtitle data into timed {@linkplain CueGroup cue groups}.
+ *
+ * <p>Instances are stateful, so samples can be fed in repeated calls to {@link #parse(byte[])}, and
+ * one or more complete {@link CueGroup} instances will be returned when enough data has been
+ * received. Due to this stateful-ness, {@link #reset()} must be called after a seek or similar
+ * discontinuity in the source data.
+ */
+@UnstableApi
+public interface SubtitleParser {
+
+  /**
+   * Parses {@code data} (and any data stored from previous invocations) and returns any resulting
+   * complete {@link CueGroup} instances.
+   *
+   * <p>Equivalent to {@link #parse(byte[], int, int) parse(data, 0, data.length)}.
+   */
+  @Nullable
+  default List<CueGroup> parse(byte[] data) {
+    return parse(data, /* offset= */ 0, data.length);
+  }
+
+  /**
+   * Parses {@code data} (and any data stored from previous invocations) and returns any resulting
+   * complete {@link CueGroup} instances.
+   *
+   * <p>Any samples not used from {@code data} will be persisted and used during subsequent calls to
+   * this method.
+   *
+   * @param data The subtitle data to parse. This must contain only complete samples. For subtitles
+   *     muxed inside a media container, a sample is usually defined by the container. For subtitles
+   *     read from a text file, a sample is usually the entire contents of the text file.
+   * @param offset The index in {@code data} to start reading from (inclusive).
+   * @param length The number of bytes to read from {@code data}.
+   * @return The {@linkplain CueGroup cue groups} parsed from {@code data} (and possibly previous
+   *     provided samples too), or null if there is insufficient data to generate a complete {@link
+   *     CueGroup}.
+   */
+  @Nullable
+  List<CueGroup> parse(byte[] data, int offset, int length);
+
+  /**
+   * Clears any data stored inside this parser from previous {@link #parse(byte[])} calls.
+   *
+   * <p>This must be called after a seek or other similar discontinuity in the source data.
+   */
+  void reset();
+}