Derive Format.frameRate for MP4 videos

Issue: #5598
PiperOrigin-RevId: 237067179

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/Mp4Extractor.java

@@ -401,21 +401,27 @@ public final class Mp4Extractor implements Extractor, SeekMap {
     for (int i = 0; i < trackCount; i++) {
       TrackSampleTable trackSampleTable = trackSampleTables.get(i);
       Track track = trackSampleTable.track;
+      long trackDurationUs =
+          track.durationUs != C.TIME_UNSET ? track.durationUs : trackSampleTable.durationUs;
+      durationUs = Math.max(durationUs, trackDurationUs);
       Mp4Track mp4Track = new Mp4Track(track, trackSampleTable,
           extractorOutput.track(i, track.type));
+
       // Each sample has up to three bytes of overhead for the start code that replaces its length.
       // Allow ten source samples per output sample, like the platform extractor.
       int maxInputSize = trackSampleTable.maximumSize + 3 * 10;
       Format format = track.format.copyWithMaxInputSize(maxInputSize);
+      if (track.type == C.TRACK_TYPE_VIDEO
+          && trackDurationUs > 0
+          && trackSampleTable.sampleCount > 1) {
+        float frameRate = trackSampleTable.sampleCount / (trackDurationUs / 1000000f);
+        format = format.copyWithFrameRate(frameRate);
+      }
       format =
           MetadataUtil.getFormatWithMetadata(
               track.type, format, udtaMetadata, mdtaMetadata, gaplessInfoHolder);
       mp4Track.trackOutput.format(format);
 
-      durationUs =
-          Math.max(
-              durationUs,
-              track.durationUs != C.TIME_UNSET ? track.durationUs : trackSampleTable.durationUs);
       if (track.type == C.TRACK_TYPE_VIDEO && firstVideoTrackIndex == C.INDEX_UNSET) {
         firstVideoTrackIndex = tracks.size();
       }

library/core/src/test/assets/mp4/sample.mp4.0.dump

@@ -12,7 +12,7 @@ track 0:
     maxInputSize = 36722
     width = 1080
     height = 720
-    frameRate = -1.0
+    frameRate = 29.970028
     rotationDegrees = 0
     pixelWidthHeightRatio = 1.0
     channelCount = -1

library/core/src/test/assets/mp4/sample.mp4.1.dump

@@ -12,7 +12,7 @@ track 0:
     maxInputSize = 36722
     width = 1080
     height = 720
-    frameRate = -1.0
+    frameRate = 29.970028
     rotationDegrees = 0
     pixelWidthHeightRatio = 1.0
     channelCount = -1

library/core/src/test/assets/mp4/sample.mp4.2.dump

@@ -12,7 +12,7 @@ track 0:
     maxInputSize = 36722
     width = 1080
     height = 720
-    frameRate = -1.0
+    frameRate = 29.970028
     rotationDegrees = 0
     pixelWidthHeightRatio = 1.0
     channelCount = -1

library/core/src/test/assets/mp4/sample.mp4.3.dump

@@ -12,7 +12,7 @@ track 0:
     maxInputSize = 36722
     width = 1080
     height = 720
-    frameRate = -1.0
+    frameRate = 29.970028
     rotationDegrees = 0
     pixelWidthHeightRatio = 1.0
     channelCount = -1