diff --git a/library/core/src/main/java/com/google/android/exoplayer2/extractor/TrackOutput.java b/library/core/src/main/java/com/google/android/exoplayer2/extractor/TrackOutput.java
index d7a1c75302..0d5a168197 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/extractor/TrackOutput.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/extractor/TrackOutput.java
@@ -119,7 +119,7 @@ public interface TrackOutput {
    * Called to write sample data to the output.
    *
    * @param data A {@link ParsableByteArray} from which to read the sample data.
-   * @param length The number of bytes to read.
+   * @param length The number of bytes to read, starting from {@code data.getPosition()}.
    */
   void sampleData(ParsableByteArray data, int length);