From 173dbc87a2665043308f22c82f2fb21df32c590f Mon Sep 17 00:00:00 2001
From: Gareth Fenn <gareth.fenn@broadcom.com>
Date: Fri, 26 Jan 2024 14:35:33 +0000
Subject: [PATCH] Seek at a chunk level when seeking to chunk start positions

This avoids issues that can arise due to the slight discrepancies between
chunk start times (obtained from the manifest of segment index) and
the timestamps of the samples contained within those chunks.
---
 .../media3/exoplayer/hls/HlsChunkSource.java  |  5 ++++
 .../exoplayer/hls/HlsSampleStreamWrapper.java | 25 ++++++++++++++++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsChunkSource.java b/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsChunkSource.java
index 9d7eb774e6..c5c506d2fa 100644
--- a/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsChunkSource.java
+++ b/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsChunkSource.java
@@ -242,6 +242,11 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     return trackGroup;
   }
 
+  /** Returns if the chunk source has independent segments. */
+  public boolean hasIndependentSegments() {
+    return independentSegments;
+  }
+
   /**
    * Sets the current track selection.
    *
diff --git a/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsSampleStreamWrapper.java b/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsSampleStreamWrapper.java
index 005ccafda5..9fd47fa5b6 100644
--- a/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsSampleStreamWrapper.java
+++ b/libraries/exoplayer_hls/src/main/java/androidx/media3/exoplayer/hls/HlsSampleStreamWrapper.java
@@ -496,8 +496,21 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
       return true;
     }
 
+    // Detect whether the seek is to the start of a chunk that's at least partially buffered.
+    @Nullable HlsMediaChunk seekToMediaChunk = null;
+    if (chunkSource.hasIndependentSegments()) {
+      for (int i = 0; i < mediaChunks.size(); i++) {
+        HlsMediaChunk mediaChunk = mediaChunks.get(i);
+        long mediaChunkStartTimeUs = mediaChunk.startTimeUs;
+        if (mediaChunkStartTimeUs == positionUs) {
+          seekToMediaChunk = mediaChunk;
+          break;
+        }
+      }
+    }
+
     // If we're not forced to reset, try and seek within the buffer.
-    if (sampleQueuesBuilt && !forceReset && seekInsideBufferUs(positionUs)) {
+    if (sampleQueuesBuilt && !forceReset && seekInsideBufferUs(positionUs, seekToMediaChunk)) {
       return false;
     }
 
@@ -1470,13 +1483,19 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    * Attempts to seek to the specified position within the sample queues.
    *
    * @param positionUs The seek position in microseconds.
+   * @param chunk Optionally the chunk to seek to.
    * @return Whether the in-buffer seek was successful.
    */
-  private boolean seekInsideBufferUs(long positionUs) {
+  private boolean seekInsideBufferUs(long positionUs, @Nullable HlsMediaChunk chunk) {
     int sampleQueueCount = sampleQueues.length;
     for (int i = 0; i < sampleQueueCount; i++) {
       SampleQueue sampleQueue = sampleQueues[i];
-      boolean seekInsideQueue = sampleQueue.seekTo(positionUs, /* allowTimeBeyondBuffer= */ false);
+      boolean seekInsideQueue;
+      if (chunk != null) {
+        seekInsideQueue = sampleQueue.seekTo(chunk.getFirstSampleIndex(i));
+      } else {
+        seekInsideQueue = sampleQueue.seekTo(positionUs, /* allowTimeBeyondBuffer= */ false);
+      }
       // If we have AV tracks then an in-queue seek is successful if the seek into every AV queue
       // is successful. We ignore whether seeks within non-AV queues are successful in this case, as
       // they may be sparse or poorly interleaved. If we only have non-AV tracks then a seek is