From 64231ee079e361477596c61956ae8b78f77ac020 Mon Sep 17 00:00:00 2001
From: ibaker <ibaker@google.com>
Date: Fri, 22 Dec 2023 08:03:49 -0800
Subject: [PATCH] Tweak
 `SubtitleTranscodingTrackOutput.ensureSampleDataCapacity`

This more closely matches the intended, documented behaviour of this
method. The previous implementation was incorrectly checking
`sampleDataEnd + newSampleSize`, but it's more correct to compare
`existingSampleDataLength + newSampleSize`, in order to handle the
case of non-zero `sampleDataStart`. We've already checked above whether
`newSampleSize` fits after `sampleDataEnd` without growing or
reshuffling the array, so no need to basically repeat that check.

In the case of handling one sample at a time, the previous
implementation resulted in `sampleData` growing by `sampleSize`
**every time** the pointers reached the end. With the new check for
`sampleDataStart == sampleDataEnd`, this is avoided by always writing
each new sample at the start of the array (because the previous sample
has already been consumed), meaning `sampleData` remains equal to
`sampleSize` without growing.

PiperOrigin-RevId: 593119927
---
 .../text/SubtitleTranscodingTrackOutput.java          | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/libraries/extractor/src/main/java/androidx/media3/extractor/text/SubtitleTranscodingTrackOutput.java b/libraries/extractor/src/main/java/androidx/media3/extractor/text/SubtitleTranscodingTrackOutput.java
index eb797e8f90..a61d274a5c 100644
--- a/libraries/extractor/src/main/java/androidx/media3/extractor/text/SubtitleTranscodingTrackOutput.java
+++ b/libraries/extractor/src/main/java/androidx/media3/extractor/text/SubtitleTranscodingTrackOutput.java
@@ -20,7 +20,6 @@ import static androidx.media3.common.util.Assertions.checkArgument;
 import static androidx.media3.common.util.Assertions.checkNotNull;
 import static androidx.media3.common.util.Assertions.checkState;
 import static androidx.media3.common.util.Assertions.checkStateNotNull;
-import static java.lang.Math.max;
 
 import androidx.annotation.Nullable;
 import androidx.media3.common.C;
@@ -151,6 +150,11 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
         SubtitleParser.OutputOptions.allCues(),
         cuesWithTiming -> outputSample(cuesWithTiming, timeUs, flags));
     sampleDataStart = sampleStart + size;
+    if (sampleDataStart == sampleDataEnd) {
+      // The array is now empty, so we can move the start and end pointers back to the start.
+      sampleDataStart = 0;
+      sampleDataEnd = 0;
+    }
   }
 
   // Clearing deprecated decode-only flag for compatibility with decoders that are still using it.
@@ -194,7 +198,10 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       return;
     }
     int existingSampleDataLength = sampleDataEnd - sampleDataStart;
-    int targetLength = max(existingSampleDataLength * 2, sampleDataEnd + newSampleSize);
+    // Make sure there's enough space for the new sample (after we move existing data to the
+    // beginning of the array).
+    int targetLength =
+        Math.max(existingSampleDataLength * 2, existingSampleDataLength + newSampleSize);
     byte[] newSampleData = targetLength <= sampleData.length ? sampleData : new byte[targetLength];
     System.arraycopy(sampleData, sampleDataStart, newSampleData, 0, existingSampleDataLength);
     sampleDataStart = 0;