Add TODO about known feature gap in ImageRenderer

PiperOrigin-RevId: 600404546
(cherry picked from commit b84104e7a1)

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/image/ImageRenderer.java

@@ -201,6 +201,7 @@ public class ImageRenderer extends BaseRenderer {
       long offsetUs,
       MediaSource.MediaPeriodId mediaPeriodId)
       throws ExoPlaybackException {
+    // TODO: b/319484746 - Take startPositionUs into account to not output images too early.
     super.onStreamChanged(formats, startPositionUs, offsetUs, mediaPeriodId);
     offsetQueue.add(offsetUs);
     inputStreamEnded = false;