diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java
index 4ae1f0c97e8..15dad9982d1 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java
@@ -244,7 +244,12 @@ import org.mozilla.gecko.gfx.GeckoSurface;
 
   private class OutputProcessor {
     private final boolean mRenderToSurface;
-    private boolean mHasOutputCapacitySet;
+    // Tracks the largest output frame size observed so far. MediaCodec's
+    // getOutputBuffer(idx).capacity() is not reliable as a max-buffer hint
+    // on modern Android (it reports the valid data range of the current
+    // frame, e.g. ~28 bytes for the first SPS/PPS), so we grow the
+    // SamplePool's default monotonically from observed info.size instead.
+    private int mMaxObservedOutputSize;
     private Queue<Output> mSentOutputs = new LinkedList<>();
     private boolean mStopped;
 
@@ -285,6 +290,14 @@ import org.mozilla.gecko.gfx.GeckoSurface;
     }
 
     private Sample obtainOutputSample(final int index, final MediaCodec.BufferInfo info) {
+      // Grow the pool's minimum-useful capacity ahead of allocation so
+      // setDefaultBufferSize sweeps any now-stranded recycled samples
+      // before obtainOutput could hand one back.
+      if (!mRenderToSurface && info.size > mMaxObservedOutputSize) {
+        mMaxObservedOutputSize = info.size;
+        mSamplePool.setOutputBufferSize(mMaxObservedOutputSize);
+      }
+
       final Sample sample = mSamplePool.obtainOutput(info);
 
       if (mRenderToSurface) {
@@ -292,14 +305,6 @@ import org.mozilla.gecko.gfx.GeckoSurface;
       }
 
       final ByteBuffer output = mCodec.getOutputBuffer(index);
-      if (!mHasOutputCapacitySet) {
-        final int capacity = output.capacity();
-        if (capacity > 0) {
-          mSamplePool.setOutputBufferSize(capacity);
-          mHasOutputCapacitySet = true;
-        }
-      }
-
       if (info.size > 0) {
         try {
           mSamplePool
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/SamplePool.java b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/SamplePool.java
index a2101b3aebd..134e01154be 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/SamplePool.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/SamplePool.java
@@ -8,6 +8,7 @@ import android.media.MediaCodec;
 import android.util.SparseArray;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 import org.mozilla.gecko.mozglue.SharedMemory;
 
@@ -26,23 +27,47 @@ final class SamplePool {
       mBufferless = bufferless;
     }
 
-    private void setDefaultBufferSize(final int size) {
+    private synchronized void setDefaultBufferSize(final int size) {
       if (mBufferless) {
         throw new IllegalStateException("Setting buffer size of a bufferless pool is not allowed");
       }
+      if (size <= mDefaultBufferSize) {
+        return;
+      }
       mDefaultBufferSize = size;
+      // Sweep: any sample admitted under a smaller default is now stranded.
+      final Iterator<Sample> it = mRecycledSamples.iterator();
+      while (it.hasNext()) {
+        final Sample s = it.next();
+        final SampleBuffer buf = mBuffers.get(s.bufferId);
+        if (buf == null || buf.capacity() < mDefaultBufferSize) {
+          it.remove();
+          disposeSample(s);
+        }
+      }
     }
 
     private synchronized Sample obtain(final int size) {
-      if (!mRecycledSamples.isEmpty()) {
-        return mRecycledSamples.remove(0);
-      }
-
       if (mBufferless) {
+        if (!mRecycledSamples.isEmpty()) {
+          return mRecycledSamples.remove(0);
+        }
         return Sample.obtain();
-      } else {
-        return allocateSampleAndBuffer(size);
       }
+      final Iterator<Sample> it = mRecycledSamples.iterator();
+      while (it.hasNext()) {
+        final Sample candidate = it.next();
+        final SampleBuffer buf = mBuffers.get(candidate.bufferId);
+        if (buf != null && buf.capacity() >= size) {
+          it.remove();
+          return candidate;
+        }
+        it.remove();
+        if (buf != null) {
+          disposeSample(candidate);
+        }
+      }
+      return allocateSampleAndBuffer(size);
     }
 
     private Sample allocateSampleAndBuffer(final int size) {