Add MappingAudioSource for just-in-time audio source creation

just_audio/README.md

@@ -399,6 +399,7 @@ Please also consider pressing the thumbs up button at the top of [this page](htt
 | looping/shuffling              | ✅      | ✅  | ✅    | ✅  | ✅      | ✅    |
 | compose audio                  | ✅      | ✅  | ✅    | ✅  |         | ✅    |
 | gapless playback               | ✅      | ✅  | ✅    |     | ✅      | ✅    |
+| mapping audio sources          | ✅      |     |       | ✅  |         |       |
 | report player errors           | ✅      | ✅  | ✅    | ✅  | ✅      | ✅    |
 | handle phonecall interruptions | ✅      | ✅  |       |     |         |       |
 | buffering/loading options      | ✅      | ✅  | ✅    |     |         |       |

just_audio/android/src/main/java/com/ryanheise/just_audio/AudioPlayer.java

@@ -31,6 +31,7 @@
 import com.google.android.exoplayer2.metadata.icy.IcyInfo;
 import com.google.android.exoplayer2.source.ClippingMediaSource;
 import com.google.android.exoplayer2.source.ConcatenatingMediaSource;
+import com.google.android.exoplayer2.source.MaskingMediaSource;
 import com.google.android.exoplayer2.source.MediaSource;
 import com.google.android.exoplayer2.source.ProgressiveMediaSource;
 import com.google.android.exoplayer2.source.ShuffleOrder;
@@ -62,7 +63,7 @@
 import java.util.Map;
 import java.util.Random;
 
-public class AudioPlayer implements MethodCallHandler, Player.Listener, MetadataOutput {
+public class AudioPlayer implements MethodCallHandler, Player.Listener, MetadataOutput, LazyMediaSourceProvider {
 
     static final String TAG = "AudioPlayer";
 
@@ -611,6 +612,17 @@ private MediaSource decodeAudioSource(final Object json) {
                             .setUri(Uri.parse((String)map.get("uri")))
                             .setMimeType(MimeTypes.APPLICATION_M3U8)
                             .build());
+        case "mapping":
+            return new MaskingMediaSource(
+                    new LazyMediaSource(
+                            this,
+                            id,
+                            new MediaItem.Builder()
+                                    .setTag(id)
+                                    .build()
+                    ),
+                    true
+            );
         case "silence":
             return new SilenceMediaSource.Factory()
                     .setDurationUs(getLong(map.get("duration")))
@@ -695,6 +707,29 @@ private DataSource.Factory buildDataSourceFactory() {
         return new DefaultDataSource.Factory(context, httpDataSourceFactory);
     }
 
+    @Override
+    public void createMediaSource(String id, LazyMediaSourceReceiver receiver) {
+        handler.post(() -> {
+            methodChannel.invokeMethod("createMappedAudioSourceSource", Collections.singletonMap("id", id), new Result() {
+                @Override
+                public void success(Object json) {
+                    final MediaSource mediaSource = json == null ? null : decodeAudioSource(json);
+                    receiver.onMediaSourceCreated(mediaSource);
+                }
+
+                @Override
+                public void error(String errorCode, String errorMessage, Object errorDetails) {
+                    throw new IllegalStateException("createMappedAudioSourceSource failed. Cannot proceed. (" + errorCode + ", " + errorMessage + ", " + errorDetails + ")");
+                }
+
+                @Override
+                public void notImplemented() {
+                    throw new IllegalArgumentException("createMappedAudioSourceSource is not implemented by the platform.");
+                }
+            });
+        });
+    }
+
     private void load(final MediaSource mediaSource, final long initialPosition, final Integer initialIndex, final Result result) {
         this.initialPos = initialPosition;
         this.initialIndex = initialIndex;

just_audio/android/src/main/java/com/ryanheise/just_audio/LazyMediaSource.java

@@ -0,0 +1,166 @@
+package com.ryanheise.just_audio;
+
+import android.os.Handler;
+
+import com.google.android.exoplayer2.MediaItem;
+import com.google.android.exoplayer2.Timeline;
+import com.google.android.exoplayer2.analytics.PlayerId;
+import com.google.android.exoplayer2.drm.DrmSessionEventListener;
+import com.google.android.exoplayer2.source.MediaPeriod;
+import com.google.android.exoplayer2.source.MediaSource;
+import com.google.android.exoplayer2.source.MediaSourceEventListener;
+import com.google.android.exoplayer2.source.SilenceMediaSource;
+import com.google.android.exoplayer2.upstream.Allocator;
+import com.google.android.exoplayer2.upstream.TransferListener;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A {@link MediaSource} that lazily defers to another {@link MediaSource} when it is required.
+ * <p>
+ * This {@link MediaSource} must be used with a {@link com.google.android.exoplayer2.source.MaskingMediaSource}.
+ */
+class LazyMediaSource implements MediaSource {
+    private final LazyMediaSourceProvider mediaSourceProvider;
+    public final String id;
+    public final MediaItem placeholderMediaItem;
+
+    private final Map<MediaSourceEventListener, Handler> pendingEventListeners = new HashMap<>();
+    private final Map<DrmSessionEventListener, Handler> pendingDrmEventListeners = new HashMap<>();
+
+    private MediaSource mediaSource;
+
+    LazyMediaSource(LazyMediaSourceProvider mediaSourceProvider, String id, MediaItem placeholderMediaItem) {
+        this.mediaSourceProvider = mediaSourceProvider;
+        this.id = id;
+        this.placeholderMediaItem = placeholderMediaItem;
+    }
+
+    @Override
+    public void addEventListener(Handler handler, MediaSourceEventListener eventListener) {
+        if (mediaSource == null) {
+            pendingEventListeners.put(eventListener, handler);
+        } else {
+            mediaSource.addEventListener(handler, eventListener);
+        }
+    }
+
+    @Override
+    public void removeEventListener(MediaSourceEventListener eventListener) {
+        if (mediaSource == null) {
+            pendingEventListeners.remove(eventListener);
+        } else {
+            mediaSource.removeEventListener(eventListener);
+        }
+    }
+
+    @Override
+    public void addDrmEventListener(Handler handler, DrmSessionEventListener eventListener) {
+        if (mediaSource == null) {
+            pendingDrmEventListeners.put(eventListener, handler);
+        } else {
+            mediaSource.addDrmEventListener(handler, eventListener);
+        }
+    }
+
+    @Override
+    public void removeDrmEventListener(DrmSessionEventListener eventListener) {
+        if (mediaSource == null) {
+            pendingDrmEventListeners.remove(eventListener);
+        } else {
+            mediaSource.removeDrmEventListener(eventListener);
+        }
+    }
+
+    @Override
+    public Timeline getInitialTimeline() {
+        if (mediaSource == null) return null;
+        return mediaSource.getInitialTimeline();
+    }
+
+    @Override
+    public boolean isSingleWindow() {
+        if (mediaSource == null) return false;
+        return mediaSource.isSingleWindow();
+    }
+
+    @Override
+    public MediaItem getMediaItem() {
+        if (mediaSource == null) {
+            return placeholderMediaItem;
+        } else {
+            return mediaSource.getMediaItem();
+        }
+    }
+
+    @Override
+    public void prepareSource(
+            MediaSourceCaller caller,
+            TransferListener mediaTransferListener,
+            PlayerId playerId
+    ) {
+        mediaSourceProvider.createMediaSource(id, (mediaSource) -> {
+            if (mediaSource == null) {
+                this.mediaSource = new SilenceMediaSource(0);
+            } else {
+                this.mediaSource = mediaSource;
+            }
+
+            for (Map.Entry<MediaSourceEventListener, Handler> entry : pendingEventListeners.entrySet()) {
+                this.mediaSource.addEventListener(entry.getValue(), entry.getKey());
+            }
+            pendingEventListeners.clear();
+            for (Map.Entry<DrmSessionEventListener, Handler> entry : pendingDrmEventListeners.entrySet()) {
+                this.mediaSource.addDrmEventListener(entry.getValue(), entry.getKey());
+            }
+            pendingDrmEventListeners.clear();
+            this.mediaSource.prepareSource(caller, mediaTransferListener, playerId);
+        });
+    }
+
+    @Override
+    public void maybeThrowSourceInfoRefreshError() throws IOException {
+        if (mediaSource == null) return;
+        mediaSource.maybeThrowSourceInfoRefreshError();
+    }
+
+    @Override
+    public void enable(MediaSourceCaller caller) {
+        if (mediaSource == null) throw new IllegalStateException();
+        mediaSource.enable(caller);
+    }
+
+    @Override
+    public MediaPeriod createPeriod(MediaPeriodId id, Allocator allocator, long startPositionUs) {
+        if (mediaSource == null) throw new IllegalStateException();
+        return mediaSource.createPeriod(id, allocator, startPositionUs);
+    }
+
+    @Override
+    public void releasePeriod(MediaPeriod mediaPeriod) {
+        if (mediaSource == null) throw new IllegalStateException();
+        mediaSource.releasePeriod(mediaPeriod);
+    }
+
+    @Override
+    public void disable(MediaSourceCaller caller) {
+        if (mediaSource == null) throw new IllegalStateException();
+        mediaSource.disable(caller);
+    }
+
+    @Override
+    public void releaseSource(MediaSourceCaller caller) {
+        if (mediaSource == null) return;
+        mediaSource.releaseSource(caller);
+    }
+}
+
+interface LazyMediaSourceReceiver {
+    void onMediaSourceCreated(MediaSource mediaSource);
+}
+
+interface LazyMediaSourceProvider {
+    void createMediaSource(String id, LazyMediaSourceReceiver receiver);
+}

just_audio/lib/just_audio.dart

@@ -1329,6 +1329,11 @@ class AudioPlayer {
       final platform = active
           ? await (_nativePlatform = _pluginPlatform.init(InitRequest(
               id: _id,
+              getAudioSourceMessage: (id) {
+                assert(_audioSources.containsKey(id),
+                    'Audio source with ID $id does not exist!');
+                return _audioSources[id]!._toMessage();
+              },
               audioLoadConfiguration: _audioLoadConfiguration?._toMessage(),
               androidAudioEffects: (_isAndroid() || _isUnitTest())
                   ? _audioPipeline.androidAudioEffects
@@ -2144,6 +2149,9 @@ abstract class IndexedAudioSource extends AudioSource {
   @override
   void _shuffle({int? initialIndex}) {}
 
+  @override
+  IndexedAudioSourceMessage _toMessage();
+
   @override
   List<IndexedAudioSource> get sequence => [this];
 
@@ -2245,7 +2253,7 @@ class ProgressiveAudioSource extends UriAudioSource {
       : super(uri, headers: headers, tag: tag, duration: duration);
 
   @override
-  AudioSourceMessage _toMessage() => ProgressiveAudioSourceMessage(
+  IndexedAudioSourceMessage _toMessage() => ProgressiveAudioSourceMessage(
       id: _id, uri: _effectiveUri.toString(), headers: headers, tag: tag);
 }
 
@@ -2269,7 +2277,7 @@ class DashAudioSource extends UriAudioSource {
       : super(uri, headers: headers, tag: tag, duration: duration);
 
   @override
-  AudioSourceMessage _toMessage() => DashAudioSourceMessage(
+  IndexedAudioSourceMessage _toMessage() => DashAudioSourceMessage(
       id: _id, uri: _effectiveUri.toString(), headers: headers, tag: tag);
 }
 
@@ -2292,7 +2300,7 @@ class HlsAudioSource extends UriAudioSource {
       : super(uri, headers: headers, tag: tag, duration: duration);
 
   @override
-  AudioSourceMessage _toMessage() => HlsAudioSourceMessage(
+  IndexedAudioSourceMessage _toMessage() => HlsAudioSourceMessage(
       id: _id, uri: _effectiveUri.toString(), headers: headers, tag: tag);
 }
 
@@ -2312,10 +2320,54 @@ class SilenceAudioSource extends IndexedAudioSource {
   }) : super(tag: tag, duration: duration);
 
   @override
-  AudioSourceMessage _toMessage() =>
+  IndexedAudioSourceMessage _toMessage() =>
       SilenceAudioSourceMessage(id: _id, duration: duration);
 }
 
+/// An [AudioSource] that maps to another [AudioSource] when it is first loaded.
+///
+/// This is useful, for example, inside a [ConcatenatingAudioSource], if an
+/// audio URL cannot be loaded until just before it is played.
+///
+/// Note that [AudioSource]s are not currently disposed of until the
+/// [AudioPlayer] completes. It is recommended to keep the [identifier] and
+/// [createAudioSource] values light - the [identifier], for example, could be a
+/// basic [Object] that points to a value in a map stored elsewhere.
+///
+/// NOTE: This is officially supported on Android and the Web only. Check
+/// [supportedOnCurrentPlatform] before using.
+class MappingAudioSource<T> extends IndexedAudioSource {
+  /// An identifier representing the [AudioSource] to be created.
+  final T identifier;
+
+  /// A function that creates the [AudioSource] to be played.
+  ///
+  /// If `null` is returned, a silent, instant sound will be used instead.
+  final Future<IndexedAudioSource?> Function(T identifier) createAudioSource;
+
+  MappingAudioSource(
+    this.identifier,
+    this.createAudioSource, {
+    dynamic tag,
+    Duration? duration,
+  })  : assert(supportedOnCurrentPlatform),
+        super(tag: tag, duration: duration);
+
+  Future<IndexedAudioSource?>? _audioSourceFuture;
+
+  @override
+  IndexedAudioSourceMessage _toMessage() => MappingAudioSourceMessage(
+        id: _id,
+        createAudioSourceMessage: () => (_audioSourceFuture ??=
+                createAudioSource(identifier).then((audioSource) =>
+                    audioSource?._setup(_player!).then((_) => audioSource)))
+            .then((audioSource) => audioSource?._toMessage()),
+      );
+
+  static bool get supportedOnCurrentPlatform =>
+      JustAudioPlatform.instance.supportsMappingAudioSource;
+}
+
 /// An [AudioSource] representing a concatenation of multiple audio sources to
 /// be played in succession. This can be used to create playlists. Playback
 /// between items will be gapless on Android, iOS and macOS, while there will
@@ -2562,7 +2614,7 @@ class ClippingAudioSource extends IndexedAudioSource {
   }
 
   @override
-  AudioSourceMessage _toMessage() => ClippingAudioSourceMessage(
+  IndexedAudioSourceMessage _toMessage() => ClippingAudioSourceMessage(
       id: _id,
       child: child._toMessage() as UriAudioSourceMessage,
       start: start,
@@ -2634,7 +2686,7 @@ abstract class StreamAudioSource extends IndexedAudioSource {
   Future<StreamAudioResponse> request([int? start, int? end]);
 
   @override
-  AudioSourceMessage _toMessage() => ProgressiveAudioSourceMessage(
+  IndexedAudioSourceMessage _toMessage() => ProgressiveAudioSourceMessage(
       id: _id, uri: _uri.toString(), headers: null, tag: tag);
 }