Add Muxer interface in muxer module

The immediate plan is to replace `Transformer Muxer interface`
with this one.
It was not straight forward to move/change `Transformer Muxer interface`
hence this intermediate step.
The follow up CL will also remove fragmented MP4 related code from
`Mp4Muxer` and move it into `FragmentedMp4Muxer implements Muxer`.

PiperOrigin-RevId: 618789265

libraries/muxer/src/main/java/androidx/media3/muxer/BasicMp4Writer.java

@@ -25,7 +25,7 @@ import static java.lang.Math.min;
 import android.media.MediaCodec.BufferInfo;
 import androidx.media3.common.Format;
 import androidx.media3.common.util.Util;
-import androidx.media3.muxer.Mp4Muxer.TrackToken;
+import androidx.media3.muxer.Muxer.TrackToken;
 import com.google.common.collect.Range;
 import java.io.FileOutputStream;
 import java.io.IOException;

libraries/muxer/src/main/java/androidx/media3/muxer/FragmentedMp4Writer.java

@@ -32,7 +32,7 @@ import android.media.MediaCodec.BufferInfo;
 import androidx.media3.common.Format;
 import androidx.media3.common.MimeTypes;
 import androidx.media3.common.util.Util;
-import androidx.media3.muxer.Mp4Muxer.TrackToken;
+import androidx.media3.muxer.Muxer.TrackToken;
 import com.google.common.collect.ImmutableList;
 import java.io.FileOutputStream;
 import java.io.IOException;

libraries/muxer/src/main/java/androidx/media3/muxer/Mp4Muxer.java

@@ -70,9 +70,7 @@ import java.nio.ByteBuffer;
  * </ul>
  */
 @UnstableApi
-public final class Mp4Muxer {
+public final class Mp4Muxer implements Muxer {
-  /** A token representing an added track. */
-  public interface TrackToken {}
 
   /** Behavior for the last sample duration. */
   @Documented
@@ -223,6 +221,22 @@ public final class Mp4Muxer {
         || metadata instanceof XmpData;
   }
 
+  /**
+   * {@inheritDoc}
+   *
+   * <p>Tracks can be added at any point before the muxer is closed, even after writing samples to
+   * other tracks.
+   *
+   * <p>The order of tracks remains same in which they are added.
+   *
+   * @param format The {@link Format} for the track.
+   * @return A unique {@link TrackToken}. It should be used in {@link #writeSampleData}.
+   */
+  @Override
+  public TrackToken addTrack(Format format) {
+    return addTrack(/* sortKey= */ 1, format);
+  }
+
   /**
    * Adds a track of the given media format.
    *
@@ -242,7 +256,7 @@ public final class Mp4Muxer {
   }
 
   /**
-   * Writes encoded sample data.
+   * {@inheritDoc}
    *
    * <p>The samples are cached and are written in batches so the caller must not change/release the
    * {@link ByteBuffer} and the {@link BufferInfo} after calling this method.
@@ -254,13 +268,14 @@ public final class Mp4Muxer {
    * @param bufferInfo The {@link BufferInfo} related to this sample.
    * @throws IOException If there is any error while writing data to the disk.
    */
+  @Override
   public void writeSampleData(TrackToken trackToken, ByteBuffer byteBuffer, BufferInfo bufferInfo)
       throws IOException {
     mp4Writer.writeSampleData(trackToken, byteBuffer, bufferInfo);
   }
 
   /**
-   * Adds metadata for the output file.
+   * {@inheritDoc}
    *
    * <p>List of supported {@linkplain Metadata.Entry metadata entries}:
    *
@@ -277,12 +292,13 @@ public final class Mp4Muxer {
    * @param metadata The {@linkplain Metadata.Entry metadata}. An {@link IllegalArgumentException}
    *     is throw if the {@linkplain Metadata.Entry metadata} is not supported.
    */
+  @Override
   public void addMetadata(Metadata.Entry metadata) {
     checkArgument(isMetadataSupported(metadata), "Unsupported metadata");
     metadataCollector.addMetadata(metadata);
   }
 
-  /** Closes the MP4 file. */
+  @Override
   public void close() throws IOException {
     mp4Writer.close();
   }

libraries/muxer/src/main/java/androidx/media3/muxer/Mp4Writer.java

@@ -22,7 +22,7 @@ import android.media.MediaCodec.BufferInfo;
 import androidx.media3.common.C;
 import androidx.media3.common.Format;
 import androidx.media3.common.MimeTypes;
-import androidx.media3.muxer.Mp4Muxer.TrackToken;
+import androidx.media3.muxer.Muxer.TrackToken;
 import com.google.common.collect.ImmutableList;
 import java.io.IOException;
 import java.nio.ByteBuffer;
@@ -41,7 +41,7 @@ import java.util.List;
 
   void close() throws IOException;
 
-  class Track implements Mp4Muxer.TrackToken, Mp4MoovStructure.TrackMetadataProvider {
+  class Track implements TrackToken, Mp4MoovStructure.TrackMetadataProvider {
     public final Format format;
     public final int sortKey;
     public final List<BufferInfo> writtenSamples;

libraries/muxer/src/main/java/androidx/media3/muxer/Muxer.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2024 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
+ *
+ *      http://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.muxer;
+
+import android.media.MediaCodec;
+import androidx.media3.common.Format;
+import androidx.media3.common.Metadata;
+import androidx.media3.common.util.UnstableApi;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+/** The muxer for producing media container files. */
+@UnstableApi
+public interface Muxer {
+  /** A token representing an added track. */
+  interface TrackToken {}
+
+  /** Adds a track of the given media format. */
+  TrackToken addTrack(Format format);
+
+  /** Writes encoded sample data. */
+  void writeSampleData(
+      TrackToken trackToken, ByteBuffer byteBuffer, MediaCodec.BufferInfo bufferInfo)
+      throws IOException;
+
+  /** Adds metadata for the output file. */
+  void addMetadata(Metadata.Entry metadata);
+
+  /** Closes the file. */
+  void close() throws IOException;
+}

libraries/muxer/src/test/java/androidx/media3/muxer/Mp4MuxerEndToEndTest.java

@@ -31,7 +31,7 @@ import androidx.media3.container.Mp4OrientationData;
 import androidx.media3.container.Mp4TimestampData;
 import androidx.media3.container.XmpData;
 import androidx.media3.extractor.mp4.Mp4Extractor;
-import androidx.media3.muxer.Mp4Muxer.TrackToken;
+import androidx.media3.muxer.Muxer.TrackToken;
 import androidx.media3.test.utils.DumpFileAsserts;
 import androidx.media3.test.utils.DumpableMp4Box;
 import androidx.media3.test.utils.FakeExtractorOutput;

libraries/muxer/src/test/java/androidx/media3/muxer/Mp4MuxerMetadataTest.java

@@ -32,7 +32,7 @@ import androidx.media3.container.Mp4TimestampData;
 import androidx.media3.container.XmpData;
 import androidx.media3.extractor.mp4.Mp4Extractor;
 import androidx.media3.extractor.text.DefaultSubtitleParserFactory;
-import androidx.media3.muxer.Mp4Muxer.TrackToken;
+import androidx.media3.muxer.Muxer.TrackToken;
 import androidx.media3.test.utils.DumpFileAsserts;
 import androidx.media3.test.utils.DumpableMp4Box;
 import androidx.media3.test.utils.FakeExtractorOutput;

libraries/transformer/src/main/java/androidx/media3/transformer/InAppMuxer.java

@@ -26,7 +26,7 @@ import androidx.media3.common.MimeTypes;
 import androidx.media3.common.util.UnstableApi;
 import androidx.media3.container.Mp4OrientationData;
 import androidx.media3.muxer.Mp4Muxer;
-import androidx.media3.muxer.Mp4Muxer.TrackToken;
+import androidx.media3.muxer.Muxer.TrackToken;
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.io.FileNotFoundException;

libraries/transformer/src/main/java/androidx/media3/transformer/Muxer.java

@@ -33,6 +33,7 @@ import java.nio.ByteBuffer;
  * finish writing to the output and return any resources to the system.
  */
 @UnstableApi
+// TODO: b/330695864 - Replace with the Muxer interface from the Muxer module.
 public interface Muxer {
 
   /** Thrown when a muxing failure occurs. */