Calculate min timestamp across tracks in the Boxes.moov method

The Boxes.moov method can do the calculation instead of caller doing
it.

PiperOrigin-RevId: 679653033

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

@@ -22,6 +22,7 @@ import static androidx.media3.muxer.ColorUtils.MEDIAFORMAT_STANDARD_TO_PRIMARIES
 import static androidx.media3.muxer.ColorUtils.MEDIAFORMAT_TRANSFER_TO_MP4_TRANSFER;
 import static androidx.media3.muxer.MuxerUtil.UNSIGNED_INT_MAX_VALUE;
 import static java.lang.Math.max;
+import static java.lang.Math.min;
 import static java.nio.charset.StandardCharsets.UTF_8;
 
 import android.media.MediaCodec;
@@ -118,7 +119,6 @@ import org.checkerframework.checker.nullness.qual.PolyNull;
   public static ByteBuffer moov(
       List<Track> tracks,
       MetadataCollector metadataCollector,
-      long minInputPtsUs,
       boolean isFragmentedMp4,
       @Mp4Muxer.LastSampleDurationBehavior int lastSampleDurationBehavior) {
     // The timestamp will always fit into a 32-bit integer. This is already validated in the
@@ -127,6 +127,15 @@ import org.checkerframework.checker.nullness.qual.PolyNull;
     int creationTimestampSeconds = (int) metadataCollector.timestampData.creationTimestampSeconds;
     int modificationTimestampSeconds =
         (int) metadataCollector.timestampData.modificationTimestampSeconds;
+    long minInputPtsUs = findMinimumPresentationTimestampUsAcrossTracks(tracks);
+
+    // For a non fragmented MP4 file, avoid writing an empty moov box.
+    // For a fragmented MP4 file, the minInputPtsUs gets ignored as the moov box is written without
+    // any sample info.
+    if (!isFragmentedMp4 && minInputPtsUs == C.TIME_UNSET) {
+      return ByteBuffer.allocate(0);
+    }
+
     List<ByteBuffer> trakBoxes = new ArrayList<>();
     List<ByteBuffer> trexBoxes = new ArrayList<>();
 
@@ -134,6 +143,7 @@ import org.checkerframework.checker.nullness.qual.PolyNull;
     long videoDurationUs = 0L;
     for (int i = 0; i < tracks.size(); i++) {
       Track track = tracks.get(i);
+      // For a non fragmented MP4 file, avoid writing an empty track.
       if (!isFragmentedMp4 && track.writtenSamples.isEmpty()) {
         continue;
       }
@@ -1830,4 +1840,15 @@ import org.checkerframework.checker.nullness.qual.PolyNull;
     return Util.scaleLargeValue(
         timestampUs, videoUnitTimebase, C.MICROS_PER_SECOND, RoundingMode.HALF_UP);
   }
+
+  private static long findMinimumPresentationTimestampUsAcrossTracks(List<Track> tracks) {
+    long minInputPtsUs = Long.MAX_VALUE;
+    for (int i = 0; i < tracks.size(); i++) {
+      Track track = tracks.get(i);
+      if (!track.writtenSamples.isEmpty()) {
+        minInputPtsUs = min(track.writtenSamples.get(0).presentationTimeUs, minInputPtsUs);
+      }
+    }
+    return minInputPtsUs != Long.MAX_VALUE ? minInputPtsUs : C.TIME_UNSET;
+  }
 }

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

@@ -202,14 +202,9 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
   private void createHeader() throws IOException {
     output.position(0L);
     output.write(Boxes.ftyp());
-    // The minInputPtsUs is actually ignored as there are no pending samples to write.
     output.write(
         Boxes.moov(
-            tracks,
+            tracks, metadataCollector, /* isFragmentedMp4= */ true, lastSampleDurationBehavior));
-            metadataCollector,
-            /* minInputPtsUs= */ 0L,
-            /* isFragmentedMp4= */ true,
-            lastSampleDurationBehavior));
   }
 
   private boolean shouldFlushPendingSamples(

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

@@ -202,7 +202,6 @@ import java.util.concurrent.atomic.AtomicBoolean;
         Boxes.moov(
             editableVideoTracks,
             editableVideoMetadataCollector,
-            findMinimumPresentationTimestampUsAcrossTracks(editableVideoTracks),
             /* isFragmentedMp4= */ false,
             lastSampleDurationBehavior);
     ByteBuffer edvdBoxHeader =
@@ -273,17 +272,6 @@ import java.util.concurrent.atomic.AtomicBoolean;
     outputFileChannel.truncate(newMoovLocation + moovBytesNeeded);
   }
 
-  private static long findMinimumPresentationTimestampUsAcrossTracks(List<Track> tracks) {
-    long minInputPtsUs = Long.MAX_VALUE;
-    for (int i = 0; i < tracks.size(); i++) {
-      Track track = tracks.get(i);
-      if (!track.writtenSamples.isEmpty()) {
-        minInputPtsUs = min(track.writtenSamples.get(0).presentationTimeUs, minInputPtsUs);
-      }
-    }
-    return minInputPtsUs;
-  }
-
   private void writeHeader() throws IOException {
     outputFileChannel.position(0L);
     outputFileChannel.write(Boxes.ftyp());
@@ -311,24 +299,9 @@ import java.util.concurrent.atomic.AtomicBoolean;
   }
 
   private ByteBuffer assembleCurrentMoovData() {
-    // Recalculate the min timestamp every time, in case some new samples have smaller timestamps.
-    long minInputPtsUs = findMinimumPresentationTimestampUsAcrossTracks(tracks);
 
-    ByteBuffer moovHeader;
+    return Boxes.moov(
-    if (minInputPtsUs != Long.MAX_VALUE) {
+        tracks, metadataCollector, /* isFragmentedMp4= */ false, lastSampleDurationBehavior);
-      moovHeader =
-          Boxes.moov(
-              tracks,
-              metadataCollector,
-              minInputPtsUs,
-              /* isFragmentedMp4= */ false,
-              lastSampleDurationBehavior);
-    } else {
-      // Skip moov box, if there are no samples.
-      moovHeader = ByteBuffer.allocate(0);
-    }
-
-    return moovHeader;
   }
 
   /**