Make sure that tracks are transcoded/transmuxed consistently

All audio tracks should either all be transcoded or all be transmuxed.
Same for video tracks.

To achieve this, simplify the behaviour of transmuxAudio/Video.

PiperOrigin-RevId: 513809287

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

@@ -122,9 +122,10 @@ public final class Composition {
      * audio track will only be transcoded if necessary.
      *
      * <p>If the input {@link Composition} contains multiple {@linkplain MediaItem media items}, all
-     * the audio tracks are transmuxed if {@code transmuxAudio} is {@code true} and exporting the
+     * the audio tracks are transcoded by default. They are all transmuxed if {@code transmuxAudio}
-     * first {@link MediaItem} doesn't require audio transcoding. Otherwise, they are all
+     * is {@code true}. Transmuxed tracks must be compatible (typically, all the {@link MediaItem}
-     * transcoded. Transmuxed tracks must be compatible and must not overlap in time.
+     * instances containing the track to transmux are concatenated in a single {@link
+     * EditedMediaItemSequence} and have the same sample format for that track).
      *
      * <p>Requesting audio transmuxing and {@linkplain #experimentalSetForceAudioTrack(boolean)
      * forcing an audio track} are not allowed together because generating silence requires
@@ -148,9 +149,10 @@ public final class Composition {
      * video track will only be transcoded if necessary.
      *
      * <p>If the input {@link Composition} contains multiple {@linkplain MediaItem media items}, all
-     * the video tracks are transmuxed if {@code transmuxVideo} is {@code true} and exporting the
+     * the video tracks are transcoded by default. They are all transmuxed if {@code transmuxVideo}
-     * first {@link MediaItem} doesn't require video transcoding. Otherwise, they are all
+     * is {@code true}. Transmuxed tracks must be compatible (typically, all the {@link MediaItem}
-     * transcoded. Transmuxed tracks must be compatible and must not overlap in time.
+     * instances containing the track to transmux are concatenated in a single {@link
+     * EditedMediaItemSequence} and have the same sample format for that track).
      *
      * @param transmuxVideo Whether to transmux the video tracks.
      * @return This builder.

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

@@ -582,8 +582,8 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       }
 
       private boolean shouldTranscodeAudio(Format inputFormat) {
-        if (editedMediaItems.size() > 1 && !composition.transmuxAudio) {
+        if (composition.sequences.size() > 1 || editedMediaItems.size() > 1) {
-          return true;
+          return !composition.transmuxAudio;
         }
         if (encoderFactory.audioNeedsEncoding()) {
           return true;
@@ -603,14 +603,13 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
         if (!firstEditedMediaItem.effects.audioProcessors.isEmpty()) {
           return true;
         }
-
         return false;
       }
 
       private boolean shouldTranscodeVideo(
           Format inputFormat, long streamStartPositionUs, long streamOffsetUs) {
-        if (editedMediaItems.size() > 1 && !composition.transmuxVideo) {
+        if (composition.sequences.size() > 1 || editedMediaItems.size() > 1) {
-          return true;
+          return !composition.transmuxVideo;
         }
         EditedMediaItem firstEditedMediaItem = editedMediaItems.get(0);
         if ((streamStartPositionUs - streamOffsetUs) != 0

libraries/transformer/src/test/java/androidx/media3/transformer/TransformerEndToEndTest.java

@@ -50,6 +50,7 @@ import androidx.media3.common.audio.AudioProcessor;
 import androidx.media3.common.audio.SonicAudioProcessor;
 import androidx.media3.common.util.Util;
 import androidx.media3.effect.Presentation;
+import androidx.media3.effect.RgbFilter;
 import androidx.media3.effect.ScaleAndRotateTransformation;
 import androidx.media3.exoplayer.source.DefaultMediaSourceFactory;
 import androidx.media3.exoplayer.source.MediaSource;
@@ -516,15 +517,16 @@ public final class TransformerEndToEndTest {
   }
 
   @Test
-  public void start_multipleMediaItemsWithEffectsAndTransmux_ignoresTransmux() throws Exception {
+  public void start_multipleMediaItemsAndTransmux_transmux() throws Exception {
     Transformer transformer = createTransformerBuilder(/* enableFallback= */ false).build();
     MediaItem mediaItem = MediaItem.fromUri(ASSET_URI_PREFIX + FILE_AUDIO_VIDEO);
     SonicAudioProcessor sonicAudioProcessor = new SonicAudioProcessor();
     sonicAudioProcessor.setPitch(2f);
+    Effect videoEffect = RgbFilter.createGrayscaleFilter();
     Effects effects =
-        new Effects(ImmutableList.of(sonicAudioProcessor), /* videoEffects= */ ImmutableList.of());
+        new Effects(ImmutableList.of(sonicAudioProcessor), ImmutableList.of(videoEffect));
     EditedMediaItem editedMediaItem =
-        new EditedMediaItem.Builder(mediaItem).setEffects(effects).setRemoveVideo(true).build();
+        new EditedMediaItem.Builder(mediaItem).setEffects(effects).build();
     EditedMediaItemSequence editedMediaItemSequence =
         new EditedMediaItemSequence(ImmutableList.of(editedMediaItem, editedMediaItem));
     Composition composition =
@@ -536,13 +538,8 @@ public final class TransformerEndToEndTest {
     transformer.start(composition, outputPath);
     TransformerTestRunner.runLooper(transformer);
 
-    // The inputs should be transcoded even though transmuxing has been requested. This is because
-    // audio effects have been added to the first MediaItem in the sequence, so the transcoding
-    // audio sample pipeline should be picked to apply these effects.
     DumpFileAsserts.assertOutput(
-        context,
+        context, testMuxer, getDumpFileName(FILE_AUDIO_VIDEO + ".concatenated"));
-        testMuxer,
-        getDumpFileName(FILE_AUDIO_VIDEO + ".concatenated_with_high_pitch_and_no_video"));
   }
 
   @Test