diff --git a/README.md b/README.md
index bf4d62b5..daed9697 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,7 @@ CameraView is a well documented, high-level library that makes capturing picture
 addressing most of the common issues and needs, and still leaving you with flexibility where needed.
 
 ```groovy
-api 'com.otaliastudios:cameraview:2.3.0'
+api 'com.otaliastudios:cameraview:2.3.1'
 ```
 
 - Fast & reliable
diff --git a/cameraview/build.gradle b/cameraview/build.gradle
index b536ef88..9d0d528a 100644
--- a/cameraview/build.gradle
+++ b/cameraview/build.gradle
@@ -3,7 +3,7 @@ apply plugin: 'com.github.dcendents.android-maven'
 apply plugin: 'com.jfrog.bintray'
 
 // Required by bintray
-version = '2.3.0'
+version = '2.3.1'
 group = 'com.otaliastudios'
 
 //region android dependencies
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera1Engine.java b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera1Engine.java
index 11db5d38..60d63cb7 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera1Engine.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera1Engine.java
@@ -97,6 +97,7 @@ public class Camera1Engine extends CameraEngine implements
 
     //region Protected APIs
 
+    @EngineThread
     @NonNull
     @Override
     protected List<Size> getPreviewStreamAvailableSizes() {
@@ -110,12 +111,13 @@ public class Camera1Engine extends CameraEngine implements
         return result;
     }
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onPreviewStreamSizeChanged() {
         restartPreview();
     }
 
+    @EngineThread
     @Override
     protected boolean collectCameraInfo(@NonNull Facing facing) {
         int internalFacing = mMapper.mapFacing(facing);
@@ -140,7 +142,7 @@ public class Camera1Engine extends CameraEngine implements
     //region Start
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     @Override
     protected Task<Void> onStartEngine() {
         try {
@@ -164,6 +166,7 @@ public class Camera1Engine extends CameraEngine implements
         return Tasks.forResult(null);
     }
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStartBind() {
@@ -187,6 +190,7 @@ public class Camera1Engine extends CameraEngine implements
         return Tasks.forResult(null);
     }
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStartPreview() {
@@ -238,6 +242,7 @@ public class Camera1Engine extends CameraEngine implements
 
     //region Stop
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStopPreview() {
@@ -256,6 +261,7 @@ public class Camera1Engine extends CameraEngine implements
         return Tasks.forResult(null);
     }
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStopBind() {
@@ -275,8 +281,8 @@ public class Camera1Engine extends CameraEngine implements
         return Tasks.forResult(null);
     }
 
+    @EngineThread
     @NonNull
-    @WorkerThread
     @Override
     protected Task<Void> onStopEngine() {
         LOG.i("onStopEngine:", "About to clean up.");
@@ -306,7 +312,7 @@ public class Camera1Engine extends CameraEngine implements
 
     //region Pictures
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onTakePicture(@NonNull PictureResult.Stub stub, boolean doMetering) {
         stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT,
@@ -316,7 +322,7 @@ public class Camera1Engine extends CameraEngine implements
         mPictureRecorder.take();
     }
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onTakePictureSnapshot(@NonNull PictureResult.Stub stub,
                                          @NonNull AspectRatio outputRatio,
@@ -337,6 +343,7 @@ public class Camera1Engine extends CameraEngine implements
 
     //region Videos
 
+    @EngineThread
     @Override
     protected void onTakeVideo(@NonNull VideoResult.Stub stub) {
         stub.rotation = getAngles().offset(Reference.SENSOR, Reference.OUTPUT,
@@ -357,7 +364,7 @@ public class Camera1Engine extends CameraEngine implements
     }
 
     @SuppressLint("NewApi")
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onTakeVideoSnapshot(@NonNull VideoResult.Stub stub,
                                        @NonNull AspectRatio outputRatio) {
@@ -765,7 +772,7 @@ public class Camera1Engine extends CameraEngine implements
     }
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private static List<Camera.Area> computeMeteringAreas(double viewClickX, double viewClickY,
                                                           int viewWidth, int viewHeight,
                                                           int sensorToDisplay) {
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera2Engine.java b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera2Engine.java
index 8995b162..a35de766 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera2Engine.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera2Engine.java
@@ -28,7 +28,6 @@ import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
 import androidx.annotation.VisibleForTesting;
-import androidx.annotation.WorkerThread;
 
 import com.google.android.gms.tasks.Task;
 import com.google.android.gms.tasks.TaskCompletionSource;
@@ -246,6 +245,17 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                         mRepeatingRequestCallback, null);
             } catch (CameraAccessException e) {
                 throw new CameraException(e, errorReason);
+            } catch (IllegalStateException e) {
+                // mSession is invalid - has been closed. This is extremely worrying because
+                // it means that the session state and getPreviewState() are not synced.
+                // This probably signals an error in the setup/teardown synchronization.
+                LOG.e("applyRepeatingRequestBuilder: session is invalid!", e,
+                        "checkStarted:", checkStarted,
+                        "currentThread:", Thread.currentThread().getName(),
+                        "previewState:", getPreviewState(),
+                        "bindState:", getBindState(),
+                        "engineState:", getEngineState());
+                throw new CameraException(CameraException.REASON_DISCONNECTED);
             }
         }
     }
@@ -286,6 +296,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     //region Protected APIs
 
+    @EngineThread
     @NonNull
     @Override
     protected List<Size> getPreviewStreamAvailableSizes() {
@@ -310,12 +321,13 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         }
     }
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onPreviewStreamSizeChanged() {
         restartBind();
     }
 
+    @EngineThread
     @Override
     protected final boolean collectCameraInfo(@NonNull Facing facing) {
         int internalFacing = mMapper.mapFacing(facing);
@@ -353,6 +365,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     //region Start
 
+    @EngineThread
     @SuppressLint("MissingPermission")
     @NonNull
     @Override
@@ -402,6 +415,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return task.getTask();
     }
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStartBind() {
@@ -525,6 +539,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return task.getTask();
     }
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStartPreview() {
@@ -569,6 +584,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     //region Stop
 
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStopPreview() {
@@ -598,7 +614,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return Tasks.forResult(null);
     }
 
-
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStopBind() {
@@ -627,7 +643,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return Tasks.forResult(null);
     }
 
-
+    @EngineThread
     @NonNull
     @Override
     protected Task<Void> onStopEngine() {
@@ -660,7 +676,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     //region Pictures
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onTakePictureSnapshot(@NonNull final PictureResult.Stub stub,
                                          @NonNull final AspectRatio outputRatio,
@@ -692,6 +708,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         }
     }
 
+    @EngineThread
     @Override
     protected void onTakePicture(@NonNull final PictureResult.Stub stub, boolean doMetering) {
         if (doMetering) {
@@ -752,7 +769,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     //region Videos
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onTakeVideo(@NonNull VideoResult.Stub stub) {
         LOG.i("onTakeVideo", "called.");
@@ -787,7 +804,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         }
     }
 
-    @WorkerThread
+    @EngineThread
     @Override
     protected void onTakeVideoSnapshot(@NonNull VideoResult.Stub stub,
                                        @NonNull AspectRatio outputRatio) {
@@ -832,7 +849,9 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     @Override
     public void onVideoRecordingEnd() {
         super.onVideoRecordingEnd();
-        boolean needsIssue549Workaround = (mVideoRecorder instanceof Full2VideoRecorder) ||
+        // SnapshotRecorder will invoke this on its own thread which is risky, but if it was a
+        // snapshot, this function returns early so its safe.
+        boolean needsIssue549Workaround = (mVideoRecorder instanceof Full2VideoRecorder) &&
                 (readCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL, -1)
                         == CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY);
         if (needsIssue549Workaround) {
@@ -843,7 +862,16 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     @Override
     public void onVideoResult(@Nullable VideoResult.Stub result, @Nullable Exception exception) {
         super.onVideoResult(result, exception);
-        maybeRestorePreviewTemplateAfterVideo();
+        // SnapshotRecorder will invoke this on its own thread, so let's post in our own thread
+        // and check camera state before trying to restore the preview. Engine might have been
+        // torn down in the engine thread while this was still being called.
+        mHandler.run(new Runnable() {
+            @Override
+            public void run() {
+                if (getBindState() < STATE_STARTED) return;
+                maybeRestorePreviewTemplateAfterVideo();
+            }
+        });
     }
 
     /**
@@ -854,6 +882,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
      * This method avoids doing this twice by checking the request tag, as set by
      * the {@link #createRepeatingRequestBuilder(int)} method.
      */
+    @EngineThread
     private void maybeRestorePreviewTemplateAfterVideo() {
         int template = (int) mRepeatingRequestBuilder.build().getTag();
         if (template != CameraDevice.TEMPLATE_PREVIEW) {
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/CameraEngine.java b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/CameraEngine.java
index 6616b0e0..2631b2b9 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/CameraEngine.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/CameraEngine.java
@@ -47,7 +47,6 @@ import androidx.annotation.CallSuper;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
-import androidx.annotation.WorkerThread;
 
 import java.io.File;
 import java.util.ArrayList;
@@ -303,7 +302,7 @@ public abstract class CameraEngine implements
 
         final CameraException cameraException = (CameraException) throwable;
         LOG.e("uncaughtException:", "Got CameraException:", cameraException,
-                "on engine state:", getEngineStateName());
+                "on engine state:", getEngineState());
         if (fromExceptionHandler) {
             // Got to restart the handler.
             thread.interrupt();
@@ -336,11 +335,6 @@ public abstract class CameraEngine implements
         return mPreviewStep.getState();
     }
 
-    @NonNull
-    private String getEngineStateName() {
-        return mEngineStep.getStateName();
-    }
-
     private boolean canStartEngine() {
         return mEngineStep.isStoppingOrStopped();
     }
@@ -375,7 +369,7 @@ public abstract class CameraEngine implements
     //region Start & Stop the engine
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private Task<Void> startEngine() {
         if (canStartEngine()) {
             mEngineStep.doStart(false, new Callable<Task<Void>>() {
@@ -398,7 +392,7 @@ public abstract class CameraEngine implements
     }
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private Task<Void> stopEngine(boolean swallowExceptions) {
         if (needsStopEngine()) {
             mEngineStep.doStop(swallowExceptions, new Callable<Task<Void>>() {
@@ -421,7 +415,7 @@ public abstract class CameraEngine implements
      * @return a task
      */
     @NonNull
-    @WorkerThread
+    @EngineThread
     protected abstract Task<Void> onStartEngine();
 
     /**
@@ -431,7 +425,7 @@ public abstract class CameraEngine implements
      * @return a task
      */
     @NonNull
-    @WorkerThread
+    @EngineThread
     protected abstract Task<Void> onStopEngine();
 
     //endregion
@@ -439,7 +433,7 @@ public abstract class CameraEngine implements
     //region Start & Stop binding
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private Task<Void> startBind() {
         if (canStartBind()) {
             mBindStep.doStart(false, new Callable<Task<Void>>() {
@@ -453,7 +447,7 @@ public abstract class CameraEngine implements
     }
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private Task<Void> stopBind(boolean swallowExceptions) {
         if (needsStopBind()) {
             mBindStep.doStop(swallowExceptions, new Callable<Task<Void>>() {
@@ -471,7 +465,7 @@ public abstract class CameraEngine implements
      * @return a task
      */
     @NonNull
-    @WorkerThread
+    @EngineThread
     protected abstract Task<Void> onStartBind();
 
     /**
@@ -481,7 +475,7 @@ public abstract class CameraEngine implements
      * @return a task
      */
     @NonNull
-    @WorkerThread
+    @EngineThread
     protected abstract Task<Void> onStopBind();
 
     @SuppressWarnings("WeakerAccess")
@@ -522,7 +516,7 @@ public abstract class CameraEngine implements
     //region Start & Stop preview
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private Task<Void> startPreview() {
         LOG.i("startPreview", "canStartPreview:", canStartPreview());
         if (canStartPreview()) {
@@ -537,7 +531,7 @@ public abstract class CameraEngine implements
     }
 
     @NonNull
-    @WorkerThread
+    @EngineThread
     private Task<Void> stopPreview(boolean swallowExceptions) {
         LOG.i("stopPreview",
                 "needsStopPreview:", needsStopPreview(),
@@ -571,7 +565,7 @@ public abstract class CameraEngine implements
      * @return a task
      */
     @NonNull
-    @WorkerThread
+    @EngineThread
     protected abstract Task<Void> onStartPreview();
 
     /**
@@ -581,7 +575,7 @@ public abstract class CameraEngine implements
      * @return a task
      */
     @NonNull
-    @WorkerThread
+    @EngineThread
     protected abstract Task<Void> onStopPreview();
 
     //endregion
@@ -643,7 +637,7 @@ public abstract class CameraEngine implements
      *
      * It basically depends on the step at which the preview stream size is actually used.
      */
-    @WorkerThread
+    @EngineThread
     protected abstract void onPreviewStreamSizeChanged();
 
     @Override
@@ -676,7 +670,7 @@ public abstract class CameraEngine implements
      * that would cause deadlocks due to us awaiting for {@link #stop()} to return.
      */
     public void destroy() {
-        LOG.i("destroy:", "state:", getEngineStateName(), "thread:", Thread.currentThread());
+        LOG.i("destroy:", "state:", getEngineState(), "thread:", Thread.currentThread());
         // Prevent CameraEngine leaks. Don't set to null, or exceptions
         // inside the standard stop() method might crash the main thread.
         mHandler.getThread().setUncaughtExceptionHandler(new NoOpExceptionHandler());
@@ -710,7 +704,7 @@ public abstract class CameraEngine implements
 
     @NonNull
     public Task<Void> start() {
-        LOG.i("Start:", "posting runnable. State:", getEngineStateName());
+        LOG.i("Start:", "posting runnable. State:", getEngineState());
         final TaskCompletionSource<Void> outTask = new TaskCompletionSource<>();
         mHandler.run(new Runnable() {
             @Override
@@ -765,7 +759,7 @@ public abstract class CameraEngine implements
 
     @NonNull
     private Task<Void> stop(final boolean swallowExceptions) {
-        LOG.i("Stop:", "posting runnable. State:", getEngineStateName());
+        LOG.i("Stop:", "posting runnable. State:", getEngineState());
         final TaskCompletionSource<Void> outTask = new TaskCompletionSource<>();
         mHandler.run(new Runnable() {
             @Override
@@ -1077,6 +1071,7 @@ public abstract class CameraEngine implements
      * @param facing the facing value
      * @return true if we have one
      */
+    @EngineThread
     protected abstract boolean collectCameraInfo(@NonNull Facing facing);
 
     /**
@@ -1256,6 +1251,7 @@ public abstract class CameraEngine implements
         });
     }
 
+    @EngineThread
     @SuppressWarnings("WeakerAccess")
     protected void onStopVideo() {
         if (mVideoRecorder != null) {
@@ -1289,19 +1285,19 @@ public abstract class CameraEngine implements
         mCallback.dispatchOnVideoRecordingEnd();
     }
 
-    @WorkerThread
+    @EngineThread
     protected abstract void onTakePicture(@NonNull PictureResult.Stub stub, boolean doMetering);
 
-    @WorkerThread
+    @EngineThread
     protected abstract void onTakePictureSnapshot(@NonNull PictureResult.Stub stub,
                                                   @NonNull AspectRatio outputRatio,
                                                   boolean doMetering);
 
-    @WorkerThread
+    @EngineThread
     protected abstract void onTakeVideoSnapshot(@NonNull VideoResult.Stub stub,
                                                 @NonNull AspectRatio outputRatio);
 
-    @WorkerThread
+    @EngineThread
     protected abstract void onTakeVideo(@NonNull VideoResult.Stub stub);
 
     //endregion
@@ -1430,9 +1426,11 @@ public abstract class CameraEngine implements
      * we can be sure that the camera is available (engineState == STARTED).
      * @return a list of available sizes for preview
      */
+    @EngineThread
     @NonNull
     protected abstract List<Size> getPreviewStreamAvailableSizes();
 
+    @EngineThread
     @NonNull
     @SuppressWarnings("WeakerAccess")
     protected final Size computePreviewStreamSize() {
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/engine/EngineThread.java b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/EngineThread.java
new file mode 100644
index 00000000..8d807c5c
--- /dev/null
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/engine/EngineThread.java
@@ -0,0 +1,7 @@
+package com.otaliastudios.cameraview.engine;
+
+/**
+ * Indicates that some action is being executed on the {@link CameraEngine} thread.
+ */
+@SuppressWarnings("WeakerAccess")
+public @interface EngineThread {}
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/overlay/OverlayLayout.java b/cameraview/src/main/java/com/otaliastudios/cameraview/overlay/OverlayLayout.java
index bed667da..3b2bd782 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/overlay/OverlayLayout.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/overlay/OverlayLayout.java
@@ -127,7 +127,7 @@ public class OverlayLayout extends FrameLayout implements Overlay {
                     // to apply some scale (typically > 1).
                     float widthScale = canvas.getWidth() / (float) getWidth();
                     float heightScale = canvas.getHeight() / (float) getHeight();
-                    LOG.i("draw",
+                    LOG.v("draw",
                             "target:", target,
                             "canvas:", canvas.getWidth() + "x" + canvas.getHeight(),
                             "view:", getWidth() + "x" + getHeight(),
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/preview/GlCameraPreview.java b/cameraview/src/main/java/com/otaliastudios/cameraview/preview/GlCameraPreview.java
index 5627303a..4e32e1ef 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/preview/GlCameraPreview.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/preview/GlCameraPreview.java
@@ -23,6 +23,7 @@ import com.otaliastudios.cameraview.size.AspectRatio;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.concurrent.CopyOnWriteArraySet;
 
 import javax.microedition.khronos.egl.EGLConfig;
 import javax.microedition.khronos.opengles.GL10;
@@ -69,8 +70,9 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
     private int mOutputTextureId = 0;
     private SurfaceTexture mInputSurfaceTexture;
     private EglViewport mOutputViewport;
-    private final Set<RendererFrameCallback> mRendererFrameCallbacks
-            = Collections.synchronizedSet(new HashSet<RendererFrameCallback>());
+    // A synchronized set was not enough to avoid crashes, probably due to external classes
+    // removing the callback while this set is being iterated. CopyOnWriteArraySet solves this.
+    private final Set<RendererFrameCallback> mRendererFrameCallbacks = new CopyOnWriteArraySet<>();
     @VisibleForTesting float mCropScaleX = 1F;
     @VisibleForTesting float mCropScaleY = 1F;
     private View mRootView;
@@ -156,11 +158,8 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
             getView().queueEvent(new Runnable() {
                 @Override
                 public void run() {
-                    // Need to synchronize when iterating the Collections.synchronizedSet
-                    synchronized (mRendererFrameCallbacks) {
-                        for (RendererFrameCallback callback : mRendererFrameCallbacks) {
-                            callback.onRendererTextureCreated(mOutputTextureId);
-                        }
+                    for (RendererFrameCallback callback : mRendererFrameCallbacks) {
+                        callback.onRendererTextureCreated(mOutputTextureId);
                     }
                 }
             });
@@ -225,11 +224,8 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
             }
             mOutputViewport.drawFrame(mInputSurfaceTexture.getTimestamp() / 1000L,
                     mOutputTextureId, mTransformMatrix);
-            synchronized (mRendererFrameCallbacks) {
-                // Need to synchronize when iterating the Collections.synchronizedSet
-                for (RendererFrameCallback callback : mRendererFrameCallbacks) {
-                    callback.onRendererFrame(mInputSurfaceTexture, mCropScaleX, mCropScaleY);
-                }
+            for (RendererFrameCallback callback : mRendererFrameCallbacks) {
+                callback.onRendererFrame(mInputSurfaceTexture, mCropScaleX, mCropScaleY);
             }
         }
     }
@@ -353,12 +349,8 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
                 if (mOutputViewport != null) {
                     mOutputViewport.setFilter(filter);
                 }
-
-                // Need to synchronize when iterating the Collections.synchronizedSet
-                synchronized (mRendererFrameCallbacks) {
-                    for (RendererFrameCallback callback : mRendererFrameCallbacks) {
-                        callback.onRendererFilterChanged(filter);
-                    }
+                for (RendererFrameCallback callback : mRendererFrameCallbacks) {
+                    callback.onRendererFilterChanged(filter);
                 }
             }
         });
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/video/SnapshotVideoRecorder.java b/cameraview/src/main/java/com/otaliastudios/cameraview/video/SnapshotVideoRecorder.java
index 814a7069..4d3cde12 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/video/SnapshotVideoRecorder.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/video/SnapshotVideoRecorder.java
@@ -241,7 +241,9 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
 
     @Override
     public void onEncodingStart() {
-        //do nothing
+        // This would be the most correct place to call dispatchVideoRecordingStart. However,
+        // after this we'll post the call on the UI thread which can take some time. To compensate
+        // this, we call dispatchVideoRecordingStart() a bit earlier in this class (onStart()).
     }
 
     @Override
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/AudioMediaEncoder.java b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/AudioMediaEncoder.java
index 2348a427..c6f7d6fb 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/AudioMediaEncoder.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/AudioMediaEncoder.java
@@ -231,11 +231,11 @@ public class AudioMediaEncoder extends MediaEncoder {
                 } else {
                     mCurrentReadBytes = mAudioRecord.read(mCurrentBuffer, mConfig.frameSize());
                 }
-                LOG.i("read thread - eos:", endOfStream, "- Read new audio frame. Bytes:",
+                LOG.v("read thread - eos:", endOfStream, "- Read new audio frame. Bytes:",
                         mCurrentReadBytes);
                 if (mCurrentReadBytes > 0) { // Good read: increase PTS.
                     increaseTime(mCurrentReadBytes, endOfStream);
-                    LOG.i("read thread - eos:", endOfStream, "- mLastTimeUs:", mLastTimeUs);
+                    LOG.v("read thread - eos:", endOfStream, "- mLastTimeUs:", mLastTimeUs);
                     mCurrentBuffer.limit(mCurrentReadBytes);
                     enqueue(mCurrentBuffer, mLastTimeUs, endOfStream);
                 } else if (mCurrentReadBytes == AudioRecord.ERROR_INVALID_OPERATION) {
@@ -358,7 +358,7 @@ public class AudioMediaEncoder extends MediaEncoder {
                 if (mInputBufferQueue.isEmpty()) {
                     skipFrames(2);
                 } else {
-                    LOG.i("encoding thread - performing", mInputBufferQueue.size(),
+                    LOG.v("encoding thread - performing", mInputBufferQueue.size(),
                             "pending operations.");
                     InputBuffer inputBuffer;
                     while ((inputBuffer = mInputBufferQueue.peek()) != null) {
@@ -408,7 +408,7 @@ public class AudioMediaEncoder extends MediaEncoder {
         private void encode(@NonNull InputBuffer buffer) {
             long executeStart = System.nanoTime() / 1000000;
 
-            LOG.i("encoding thread - performing pending operation for timestamp:",
+            LOG.v("encoding thread - performing pending operation for timestamp:",
                     buffer.timestamp, "- encoding.");
             // NOTE: this copy is prob. the worst part here for performance
             buffer.data.put(buffer.source);
@@ -417,7 +417,7 @@ public class AudioMediaEncoder extends MediaEncoder {
             encodeInputBuffer(buffer);
             boolean eos = buffer.isEndOfStream;
             mInputBufferPool.recycle(buffer);
-            LOG.i("encoding thread - performing pending operation for timestamp:",
+            LOG.v("encoding thread - performing pending operation for timestamp:",
                     buffer.timestamp, "- draining.");
             // NOTE: can consider calling this drainOutput on yet another thread, which would let us
             // use an even smaller BUFFER_POOL_MAX_SIZE without losing audio frames. But this way
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoder.java b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoder.java
index 8ce51f09..df5d9118 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoder.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoder.java
@@ -397,7 +397,7 @@ public abstract class MediaEncoder {
     @SuppressLint("LogNotTimber")
     @SuppressWarnings("WeakerAccess")
     protected final void drainOutput(boolean drainAll) {
-        LOG.i(mName, "DRAINING - EOS:", drainAll);
+        LOG.v(mName, "DRAINING - EOS:", drainAll);
         if (mMediaCodec == null) {
             LOG.e("drain() was called before prepare() or after releasing.");
             return;
@@ -459,7 +459,7 @@ public abstract class MediaEncoder {
                             + mLastTimeUs - mFirstTimeUs;
 
                     // Write.
-                    LOG.i(mName, "DRAINING - About to write(). Adjusted presentation:",
+                    LOG.v(mName, "DRAINING - About to write(). Adjusted presentation:",
                             mBufferInfo.presentationTimeUs);
                     OutputBuffer buffer = mOutputBufferPool.get();
                     //noinspection ConstantConditions
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoderEngine.java b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoderEngine.java
index 7ca3eb14..744bf6a6 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoderEngine.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/MediaEncoderEngine.java
@@ -186,7 +186,7 @@ public class MediaEncoderEngine {
      */
     @SuppressWarnings("SameParameterValue")
     public final void notify(final String event, final Object data) {
-        LOG.i("Passing event to encoders:", event);
+        LOG.v("Passing event to encoders:", event);
         for (MediaEncoder encoder : mEncoders) {
             encoder.notify(event, data);
         }
diff --git a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/TextureMediaEncoder.java b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/TextureMediaEncoder.java
index 4d30dc41..5730d590 100644
--- a/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/TextureMediaEncoder.java
+++ b/cameraview/src/main/java/com/otaliastudios/cameraview/video/encoding/TextureMediaEncoder.java
@@ -124,7 +124,7 @@ public class TextureMediaEncoder extends VideoMediaEncoder<TextureConfig> {
             // Always render the first few frames, or muxer fails.
             return true;
         } else if (getPendingEvents(FRAME_EVENT) > 2) {
-            LOG.w("shouldRenderFrame - Dropping, we already have too many pending events:",
+            LOG.v("shouldRenderFrame - Dropping, we already have too many pending events:",
                     getPendingEvents(FRAME_EVENT));
             return false;
         } else {
@@ -177,14 +177,14 @@ public class TextureMediaEncoder extends VideoMediaEncoder<TextureConfig> {
         }
 
         // First, drain any previous data.
-        LOG.i("onEvent -",
+        LOG.v("onEvent -",
                 "frameNumber:", mFrameNumber,
                 "timestampUs:", frame.timestampUs(),
                 "- draining.");
         drainOutput(false);
 
         // Then draw on the surface.
-        LOG.i("onEvent -",
+        LOG.v("onEvent -",
                 "frameNumber:", mFrameNumber,
                 "timestampUs:", frame.timestampUs(),
                 "- rendering.");
diff --git a/demo/build.gradle b/demo/build.gradle
index bbf6cff8..fe41eebd 100644
--- a/demo/build.gradle
+++ b/demo/build.gradle
@@ -2,7 +2,6 @@ apply plugin: 'com.android.application'
 
 android {
     compileSdkVersion rootProject.ext.compileSdkVersion
-    // buildToolsVersion rootProject.ext.buildToolsVersion
 
     defaultConfig {
         applicationId "com.otaliastudios.cameraview.demo"
@@ -23,6 +22,6 @@ android {
 
 dependencies {
     implementation project(':cameraview')
-    implementation 'androidx.appcompat:appcompat:1.1.0-rc01'
-    implementation 'com.google.android.material:material:1.1.0-alpha09'
+    implementation 'androidx.appcompat:appcompat:1.1.0'
+    implementation 'com.google.android.material:material:1.1.0-beta01'
 }
diff --git a/demo/src/main/java/com/otaliastudios/cameraview/demo/CameraActivity.java b/demo/src/main/java/com/otaliastudios/cameraview/demo/CameraActivity.java
index 644afa6c..50508a71 100644
--- a/demo/src/main/java/com/otaliastudios/cameraview/demo/CameraActivity.java
+++ b/demo/src/main/java/com/otaliastudios/cameraview/demo/CameraActivity.java
@@ -190,12 +190,6 @@ public class CameraActivity extends AppCompatActivity implements View.OnClickLis
                 OptionView view = (OptionView) group.getChildAt(i);
                 view.onCameraOpened(camera, options);
             }
-            camera.addFrameProcessor(new FrameProcessor() {
-                @Override
-                public void process(@NonNull Frame frame) {
-
-                }
-            });
         }
 
         @Override
diff --git a/docs/_posts/2018-12-20-changelog.md b/docs/_posts/2018-12-20-changelog.md
index 4e3811d9..6d4850d1 100644
--- a/docs/_posts/2018-12-20-changelog.md
+++ b/docs/_posts/2018-12-20-changelog.md
@@ -8,6 +8,13 @@ order: 3
 
 New versions are released through GitHub, so the reference page is the [GitHub Releases](https://github.com/natario1/CameraView/releases) page.
 
+### v2.3.1
+
+- [Video] Improvement: better timing for `onVideoRecordingStart()` thanks to [@agrawalsuneet][agrawalsuneet] ([#632][632])
+- [Video, Camera1] Fix: fixed video errors when starting on specific devices ([#617][617])
+- [Video] Fix: fixed crash when closing the app during video snapshots ([#630][630])
+- [Preview] Fix: fixed crash when using `GL_SURFACE` ([#630][630])
+
 ## v2.3.0
 
 - [Camera2, Metering] New: `startAutoFocus` is much more powerful and does 3A metering (AF, AE, AWB) ([#574][574])
@@ -320,3 +327,6 @@ https://github.com/natario1/CameraView/compare/v1.2.3...v1.3.0
 [574]: https://github.com/natario1/CameraView/pull/574
 [580]: https://github.com/natario1/CameraView/pull/580
 [588]: https://github.com/natario1/CameraView/pull/588
+[617]: https://github.com/natario1/CameraView/pull/617
+[630]: https://github.com/natario1/CameraView/pull/630
+[632]: https://github.com/natario1/CameraView/pull/632
diff --git a/docs/_posts/2018-12-20-install.md b/docs/_posts/2018-12-20-install.md
index f1eb35d0..6757bc83 100644
--- a/docs/_posts/2018-12-20-install.md
+++ b/docs/_posts/2018-12-20-install.md
@@ -24,7 +24,7 @@ allprojects {
 Then simply download the latest version:
 
 ```groovy
-api 'com.otaliastudios:cameraview:2.3.0'
+api 'com.otaliastudios:cameraview:2.3.1'
 ```
 
 No other configuration steps are needed.
\ No newline at end of file