Merge pull request #4373 from priankakariatyml:ios-object-detector-async-fixes

PiperOrigin-RevId: 530233608

mediapipe/tasks/ios/common/utils/sources/NSString+Helpers.h

@@ -24,6 +24,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (NSString *)stringWithCppString:(std::string)text;
 
++ (NSString *)uuidString;
 @end
 
 NS_ASSUME_NONNULL_END

mediapipe/tasks/ios/common/utils/sources/NSString+Helpers.mm

@@ -24,4 +24,8 @@
   return [NSString stringWithCString:text.c_str() encoding:[NSString defaultCStringEncoding]];
 }
 
++ (NSString *)uuidString {
+  return [[NSUUID UUID] UUIDString];
+}
+
 @end

mediapipe/tasks/ios/components/containers/sources/MPPDetection.m

@@ -28,7 +28,12 @@
   return self;
 }
 
-// TODO: Implement hash
+- (NSUInteger)hash {
+  NSUInteger nonNullPropertiesHash =
+      @(self.location.x).hash ^ @(self.location.y).hash ^ @(self.score).hash;
+
+  return self.label ? nonNullPropertiesHash ^ self.label.hash : nonNullPropertiesHash;
+}
 
 - (BOOL)isEqual:(nullable id)object {
   if (!object) {

mediapipe/tasks/ios/test/vision/image_classifier/MPPImageClassifierTests.m

@@ -453,8 +453,8 @@ static NSString *const kExpectedErrorDomain = @"com.google.mediapipe.tasks";
                                            code:MPPTasksErrorCodeInvalidArgumentError
                                        userInfo:@{
                                          NSLocalizedDescriptionKey :
-                                             @"The vision task is in image or video mode, a "
+                                             @"The vision task is in image or video mode. The "
-                                             @"user-defined result callback should not be provided."
+                                             @"delegate must not be set in the task's options."
                                        }]];
   }
 }
@@ -470,8 +470,10 @@ static NSString *const kExpectedErrorDomain = @"com.google.mediapipe.tasks";
                                                 code:MPPTasksErrorCodeInvalidArgumentError
                                             userInfo:@{
                                               NSLocalizedDescriptionKey :
-                                                  @"The vision task is in live stream mode, a "
+                                                  @"The vision task is in live stream mode. An "
-                                                  @"user-defined result callback must be provided."
+                                                  @"object must be set as the delegate of the task "
+                                                  @"in its options to ensure asynchronous delivery "
+                                                  @"of results."
                                             }]];
 }
 

mediapipe/tasks/ios/test/vision/object_detector/MPPObjectDetectorTests.m

@@ -25,6 +25,8 @@ static NSDictionary *const kCatsAndDogsRotatedImage =
 static NSString *const kExpectedErrorDomain = @"com.google.mediapipe.tasks";
 static const float pixelDifferenceTolerance = 10.0f;
 static const float scoreDifferenceTolerance = 0.02f;
+static NSString *const kLiveStreamTestsDictObjectDetectorKey = @"object_detector";
+static NSString *const kLiveStreamTestsDictExpectationKey = @"expectation";
 
 #define AssertEqualErrors(error, expectedError)                                               \
   XCTAssertNotNil(error);                                                                     \
@@ -58,7 +60,10 @@ static const float scoreDifferenceTolerance = 0.02f;
   XCTAssertEqualWithAccuracy(boundingBox.size.height, expectedBoundingBox.size.height, \
                              pixelDifferenceTolerance, @"index i = %d", idx);
 
-@interface MPPObjectDetectorTests : XCTestCase
+@interface MPPObjectDetectorTests : XCTestCase <MPPObjectDetectorLiveStreamDelegate> {
+  NSDictionary *liveStreamSucceedsTestDict;
+  NSDictionary *outOfOrderTimestampTestDict;
+}
 @end
 
 @implementation MPPObjectDetectorTests
@@ -446,31 +451,28 @@ static const float scoreDifferenceTolerance = 0.02f;
 
 #pragma mark Running Mode Tests
 
-- (void)testCreateObjectDetectorFailsWithResultListenerInNonLiveStreamMode {
+- (void)testCreateObjectDetectorFailsWithDelegateInNonLiveStreamMode {
   MPPRunningMode runningModesToTest[] = {MPPRunningModeImage, MPPRunningModeVideo};
   for (int i = 0; i < sizeof(runningModesToTest) / sizeof(runningModesToTest[0]); i++) {
     MPPObjectDetectorOptions *options = [self objectDetectorOptionsWithModelName:kModelName];
 
     options.runningMode = runningModesToTest[i];
-    options.completion =
+    options.objectDetectorLiveStreamDelegate = self;
-        ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-        };
 
     [self
         assertCreateObjectDetectorWithOptions:options
                        failsWithExpectedError:
-                           [NSError
+                           [NSError errorWithDomain:kExpectedErrorDomain
-                               errorWithDomain:kExpectedErrorDomain
                                                code:MPPTasksErrorCodeInvalidArgumentError
                                            userInfo:@{
                                              NSLocalizedDescriptionKey :
-                                            @"The vision task is in image or video mode, a "
+                                                 @"The vision task is in image or video mode. The "
-                                            @"user-defined result callback should not be provided."
+                                                 @"delegate must not be set in the task's options."
                                            }]];
   }
 }
 
-- (void)testCreateObjectDetectorFailsWithMissingResultListenerInLiveStreamMode {
+- (void)testCreateObjectDetectorFailsWithMissingDelegateInLiveStreamMode {
   MPPObjectDetectorOptions *options = [self objectDetectorOptionsWithModelName:kModelName];
 
   options.runningMode = MPPRunningModeLiveStream;
@@ -481,8 +483,10 @@ static const float scoreDifferenceTolerance = 0.02f;
                                                code:MPPTasksErrorCodeInvalidArgumentError
                                            userInfo:@{
                                              NSLocalizedDescriptionKey :
-                                                 @"The vision task is in live stream mode, a "
+                                                 @"The vision task is in live stream mode. An "
-                                                 @"user-defined result callback must be provided."
+                                                 @"object must be set as the delegate of the task "
+                                                 @"in its options to ensure asynchronous delivery "
+                                                 @"of results."
                                            }]];
 }
 
@@ -563,10 +567,7 @@ static const float scoreDifferenceTolerance = 0.02f;
   MPPObjectDetectorOptions *options = [self objectDetectorOptionsWithModelName:kModelName];
 
   options.runningMode = MPPRunningModeLiveStream;
-  options.completion =
+  options.objectDetectorLiveStreamDelegate = self;
-      ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-
-      };
 
   MPPObjectDetector *objectDetector = [self objectDetectorWithOptionsSucceeds:options];
 
@@ -631,23 +632,17 @@ static const float scoreDifferenceTolerance = 0.02f;
   options.maxResults = maxResults;
 
   options.runningMode = MPPRunningModeLiveStream;
+  options.objectDetectorLiveStreamDelegate = self;
 
   XCTestExpectation *expectation = [[XCTestExpectation alloc]
       initWithDescription:@"detectWithOutOfOrderTimestampsAndLiveStream"];
   expectation.expectedFulfillmentCount = 1;
 
-  options.completion =
-      ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-        [self assertObjectDetectionResult:result
-                  isEqualToExpectedResult:
-                      [MPPObjectDetectorTests
-                          expectedDetectionResultForCatsAndDogsImageWithTimestampInMilliseconds:
-                              timestampInMilliseconds]
-                  expectedDetectionsCount:maxResults];
-        [expectation fulfill];
-      };
-
   MPPObjectDetector *objectDetector = [self objectDetectorWithOptionsSucceeds:options];
+  liveStreamSucceedsTestDict = @{
+    kLiveStreamTestsDictObjectDetectorKey : objectDetector,
+    kLiveStreamTestsDictExpectationKey : expectation
+  };
 
   MPPImage *image = [self imageWithFileInfo:kCatsAndDogsImage];
 
@@ -664,7 +659,9 @@ static const float scoreDifferenceTolerance = 0.02f;
                             @"INVALID_ARGUMENT: Input timestamp must be monotonically increasing."
                       }];
   AssertEqualErrors(error, expectedError);
-  [self waitForExpectations:@[ expectation ] timeout:1.0];
+
+  NSTimeInterval timeout = 0.5f;
+  [self waitForExpectations:@[ expectation ] timeout:timeout];
 }
 
 - (void)testDetectWithLiveStreamModeSucceeds {
@@ -693,19 +690,15 @@ static const float scoreDifferenceTolerance = 0.02f;
   expectation.expectedFulfillmentCount = iterationCount + 1;
   expectation.inverted = YES;
 
-  options.completion =
+  options.objectDetectorLiveStreamDelegate = self;
-      ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-        [self assertObjectDetectionResult:result
-                  isEqualToExpectedResult:
-                      [MPPObjectDetectorTests
-                          expectedDetectionResultForCatsAndDogsImageWithTimestampInMilliseconds:
-                              timestampInMilliseconds]
-                  expectedDetectionsCount:maxResults];
-        [expectation fulfill];
-      };
 
   MPPObjectDetector *objectDetector = [self objectDetectorWithOptionsSucceeds:options];
 
+  liveStreamSucceedsTestDict = @{
+    kLiveStreamTestsDictObjectDetectorKey : objectDetector,
+    kLiveStreamTestsDictExpectationKey : expectation
+  };
+
   // TODO: Mimic initialization from CMSampleBuffer as live stream mode is most likely to be used
   // with the iOS camera. AVCaptureVideoDataOutput sample buffer delegates provide frames of type
   // `CMSampleBuffer`.
@@ -715,7 +708,28 @@ static const float scoreDifferenceTolerance = 0.02f;
     XCTAssertTrue([objectDetector detectAsyncInImage:image timestampInMilliseconds:i error:nil]);
   }
 
-  [self waitForExpectations:@[ expectation ] timeout:0.5];
+  NSTimeInterval timeout = 0.5f;
+  [self waitForExpectations:@[ expectation ] timeout:timeout];
+}
+
+#pragma mark MPPObjectDetectorLiveStreamDelegate Methods
+- (void)objectDetector:(MPPObjectDetector *)objectDetector
+    didFinishDetectionWithResult:(MPPObjectDetectionResult *)objectDetectionResult
+         timestampInMilliseconds:(NSInteger)timestampInMilliseconds
+                           error:(NSError *)error {
+  NSInteger maxResults = 4;
+  [self assertObjectDetectionResult:objectDetectionResult
+            isEqualToExpectedResult:
+                [MPPObjectDetectorTests
+                    expectedDetectionResultForCatsAndDogsImageWithTimestampInMilliseconds:
+                        timestampInMilliseconds]
+            expectedDetectionsCount:maxResults];
+
+  if (objectDetector == outOfOrderTimestampTestDict[kLiveStreamTestsDictObjectDetectorKey]) {
+    [outOfOrderTimestampTestDict[kLiveStreamTestsDictExpectationKey] fulfill];
+  } else if (objectDetector == liveStreamSucceedsTestDict[kLiveStreamTestsDictObjectDetectorKey]) {
+    [liveStreamSucceedsTestDict[kLiveStreamTestsDictExpectationKey] fulfill];
+  }
 }
 
 @end

mediapipe/tasks/ios/vision/core/BUILD

@@ -58,6 +58,7 @@ objc_library(
         "//mediapipe/framework/formats:rect_cc_proto",
         "//mediapipe/tasks/ios/common:MPPCommon",
         "//mediapipe/tasks/ios/common/utils:MPPCommonUtils",
+        "//mediapipe/tasks/ios/common/utils:NSStringHelpers",
         "//mediapipe/tasks/ios/core:MPPTaskRunner",
         "//third_party/apple_frameworks:UIKit",
         "@com_google_absl//absl/status:statusor",

mediapipe/tasks/ios/vision/core/sources/MPPVisionTaskRunner.h

@@ -141,6 +141,20 @@ NS_ASSUME_NONNULL_BEGIN
                                   (mediapipe::tasks::core::PacketsCallback)packetsCallback
                                         error:(NSError **)error NS_UNAVAILABLE;
 
+/**
+ * This method returns a unique dispatch queue name by adding the given suffix and a `UUID` to the
+ * pre-defined queue name prefix for vision tasks. The vision tasks can use this method to get
+ * unique dispatch queue names which are consistent with other vision tasks.
+ * Dispatch queue names need not be unique, but for easy debugging we ensure that the queue names
+ * are unique.
+ *
+ * @param suffix A suffix that identifies a dispatch queue's functionality.
+ *
+ * @return A unique dispatch queue name by adding the given suffix and a `UUID` to the pre-defined
+ * queue name prefix for vision tasks.
+ */
++ (const char *)uniqueDispatchQueueNameWithSuffix:(NSString *)suffix;
+
 - (instancetype)init NS_UNAVAILABLE;
 
 + (instancetype)new NS_UNAVAILABLE;

mediapipe/tasks/ios/vision/core/sources/MPPVisionTaskRunner.mm

@@ -16,6 +16,7 @@
 
 #import "mediapipe/tasks/ios/common/sources/MPPCommon.h"
 #import "mediapipe/tasks/ios/common/utils/sources/MPPCommonUtils.h"
+#import "mediapipe/tasks/ios/common/utils/sources/NSString+Helpers.h"
 
 #include "absl/status/statusor.h"
 
@@ -37,6 +38,8 @@ static const NSInteger kMPPOrientationDegreesDown = -180;
 /** Rotation degrees for a 90 degree rotation to the left. */
 static const NSInteger kMPPOrientationDegreesLeft = -270;
 
+static NSString *const kTaskPrefix = @"com.mediapipe.tasks.vision";
+
 @interface MPPVisionTaskRunner () {
   MPPRunningMode _runningMode;
 }
@@ -54,18 +57,21 @@ static const NSInteger kMPPOrientationDegreesLeft = -270;
       if (packetsCallback) {
         [MPPCommonUtils createCustomError:error
                                  withCode:MPPTasksErrorCodeInvalidArgumentError
-                              description:@"The vision task is in image or video mode, a "
+                              description:@"The vision task is in image or video mode. The "
-                                          @"user-defined result callback should not be provided."];
+                                          @"delegate must not be set in the task's options."];
         return nil;
       }
       break;
     }
     case MPPRunningModeLiveStream: {
       if (!packetsCallback) {
-        [MPPCommonUtils createCustomError:error
+        [MPPCommonUtils
+            createCustomError:error
                      withCode:MPPTasksErrorCodeInvalidArgumentError
-                              description:@"The vision task is in live stream mode, a user-defined "
+                  description:
-                                          @"result callback must be provided."];
+                      @"The vision task is in live stream mode. An object must be set as the "
+                      @"delegate of the task in its options to ensure asynchronous delivery of "
+                      @"results."];
         return nil;
       }
       break;
@@ -197,4 +203,9 @@ static const NSInteger kMPPOrientationDegreesLeft = -270;
   return [self sendPacketMap:packetMap error:error];
 }
 
++ (const char *)uniqueDispatchQueueNameWithSuffix:(NSString *)suffix {
+  return [NSString stringWithFormat:@"%@.%@_%@", kTaskPrefix, suffix, [NSString uuidString]]
+      .UTF8String;
+}
+
 @end

mediapipe/tasks/ios/vision/core/utils/sources/MPPImage+Utils.mm

@@ -162,6 +162,7 @@ using ::mediapipe::ImageFrame;
   OSType pixelBufferFormat = CVPixelBufferGetPixelFormatType(pixelBuffer);
 
   switch (pixelBufferFormat) {
+    case kCVPixelFormatType_32RGBA:
     case kCVPixelFormatType_32BGRA: {
       return [MPPCVPixelBufferUtils rgbImageFrameFromCVPixelBuffer:pixelBuffer error:error];
     }
@@ -169,7 +170,8 @@ using ::mediapipe::ImageFrame;
       [MPPCommonUtils createCustomError:error
                                withCode:MPPTasksErrorCodeInvalidArgumentError
                             description:@"Unsupported pixel format for CVPixelBuffer. Supported "
-                                        @"pixel format types are kCVPixelFormatType_32BGRA"];
+                                        @"pixel format types are kCVPixelFormatType_32BGRA and "
+                                        @"kCVPixelFormatType_32RGBA"];
     }
   }
 

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetector.h

@@ -96,6 +96,15 @@ NS_SWIFT_NAME(ObjectDetector)
  * `MPPImage`. Only use this method when the `MPPObjectDetector` is created with
  * `MPPRunningModeImage`.
  *
+ * This method supports classification of RGBA images. If your `MPPImage` has a source type of
+ * `MPPImageSourceTypePixelBuffer` or `MPPImageSourceTypeSampleBuffer`, the underlying pixel buffer
+ * must have one of the following pixel format types:
+ * 1. kCVPixelFormatType_32BGRA
+ * 2. kCVPixelFormatType_32RGBA
+ *
+ * If your `MPPImage` has a source type of `MPPImageSourceTypeImage` ensure that the color space is
+ * RGB with an Alpha channel.
+ *
  * @param image The `MPPImage` on which object detection is to be performed.
  * @param error An optional error parameter populated when there is an error in performing object
  * detection on the input image.
@@ -115,6 +124,15 @@ NS_SWIFT_NAME(ObjectDetector)
  * the provided `MPPImage`. Only use this method when the `MPPObjectDetector` is created with
  * `MPPRunningModeVideo`.
  *
+ * This method supports classification of RGBA images. If your `MPPImage` has a source type of
+ * `MPPImageSourceTypePixelBuffer` or `MPPImageSourceTypeSampleBuffer`, the underlying pixel buffer
+ * must have one of the following pixel format types:
+ * 1. kCVPixelFormatType_32BGRA
+ * 2. kCVPixelFormatType_32RGBA
+ *
+ * If your `MPPImage` has a source type of `MPPImageSourceTypeImage` ensure that the color space is
+ * RGB with an Alpha channel.
+ *
  * @param image The `MPPImage` on which object detection is to be performed.
  * @param timestampInMilliseconds The video frame's timestamp (in milliseconds). The input
  * timestamps must be monotonically increasing.
@@ -135,12 +153,28 @@ NS_SWIFT_NAME(ObjectDetector)
  * Sends live stream image data of type `MPPImage` to perform object detection using the whole
  * image as region of interest. Rotation will be applied according to the `orientation` property of
  * the provided `MPPImage`. Only use this method when the `MPPObjectDetector` is created with
- * `MPPRunningModeLiveStream`. Results are provided asynchronously via the `completion` callback
+ * `MPPRunningModeLiveStream`.
- * provided in the `MPPObjectDetectorOptions`.
+ *
+ * The object which needs to be continuously notified of the available results of object
+ * detection must confirm to `MPPObjectDetectorLiveStreamDelegate` protocol and implement the
+ * `objectDetector:didFinishDetectionWithResult:timestampInMilliseconds:error:` delegate method.
  *
  * It's required to provide a timestamp (in milliseconds) to indicate when the input image is sent
  * to the object detector. The input timestamps must be monotonically increasing.
  *
+ * This method supports classification of RGBA images. If your `MPPImage` has a source type of
+ * `MPPImageSourceTypePixelBuffer` or `MPPImageSourceTypeSampleBuffer`, the underlying pixel buffer
+ * must have one of the following pixel format types:
+ * 1. kCVPixelFormatType_32BGRA
+ * 2. kCVPixelFormatType_32RGBA
+ *
+ * If the input `MPPImage` has a source type of `MPPImageSourceTypeImage` ensure that the color
+ * space is RGB with an Alpha channel.
+ *
+ * If this method is used for classifying live camera frames using `AVFoundation`, ensure that you
+ * request `AVCaptureVideoDataOutput` to output frames in `kCMPixelFormat_32RGBA` using its
+ * `videoSettings` property.
+ *
  * @param image A live stream image data of type `MPPImage` on which object detection is to be
  * performed.
  * @param timestampInMilliseconds The timestamp (in milliseconds) which indicates when the input

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetector.mm

@@ -37,8 +37,8 @@ static NSString *const kImageOutStreamName = @"image_out";
 static NSString *const kImageTag = @"IMAGE";
 static NSString *const kNormRectStreamName = @"norm_rect_in";
 static NSString *const kNormRectTag = @"NORM_RECT";
-
 static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorGraph";
+static NSString *const kTaskName = @"objectDetector";
 
 #define InputPacketMap(imagePacket, normalizedRectPacket) \
   {                                                       \
@@ -51,6 +51,7 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
   /** iOS Vision Task Runner */
   MPPVisionTaskRunner *_visionTaskRunner;
 }
+@property(nonatomic, weak) id<MPPObjectDetectorLiveStreamDelegate> objectDetectorLiveStreamDelegate;
 @end
 
 @implementation MPPObjectDetector
@@ -78,11 +79,37 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
 
     PacketsCallback packetsCallback = nullptr;
 
-    if (options.completion) {
+    if (options.objectDetectorLiveStreamDelegate) {
+      _objectDetectorLiveStreamDelegate = options.objectDetectorLiveStreamDelegate;
+
+      // Capturing `self` as weak in order to avoid `self` being kept in memory
+      // and cause a retain cycle, after self is set to `nil`.
+      MPPObjectDetector *__weak weakSelf = self;
+
+      // Create a private serial dispatch queue in which the delegate method will be called
+      // asynchronously. This is to ensure that if the client performs a long running operation in
+      // the delegate method, the queue on which the C++ callbacks is invoked is not blocked and is
+      // freed up to continue with its operations.
+      dispatch_queue_t callbackQueue = dispatch_queue_create(
+          [MPPVisionTaskRunner uniqueDispatchQueueNameWithSuffix:kTaskName], NULL);
       packetsCallback = [=](absl::StatusOr<PacketMap> statusOrPackets) {
+        if (!weakSelf) {
+          return;
+        }
+        if (![weakSelf.objectDetectorLiveStreamDelegate
+                respondsToSelector:@selector
+                (objectDetector:didFinishDetectionWithResult:timestampInMilliseconds:error:)]) {
+          return;
+        }
+
         NSError *callbackError = nil;
         if (![MPPCommonUtils checkCppError:statusOrPackets.status() toError:&callbackError]) {
-          options.completion(nil, Timestamp::Unset().Value(), callbackError);
+          dispatch_async(callbackQueue, ^{
+            [weakSelf.objectDetectorLiveStreamDelegate objectDetector:weakSelf
+                                         didFinishDetectionWithResult:nil
+                                              timestampInMilliseconds:Timestamp::Unset().Value()
+                                                                error:callbackError];
+          });
           return;
         }
 
@@ -95,10 +122,15 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
             objectDetectionResultWithDetectionsPacket:statusOrPackets.value()[kDetectionsStreamName
                                                                                   .cppString]];
 
-        options.completion(result,
+        NSInteger timeStampInMilliseconds =
             outputPacketMap[kImageOutStreamName.cppString].Timestamp().Value() /
-                               kMicroSecondsPerMilliSecond,
+            kMicroSecondsPerMilliSecond;
-                           callbackError);
+        dispatch_async(callbackQueue, ^{
+          [weakSelf.objectDetectorLiveStreamDelegate objectDetector:weakSelf
+                                       didFinishDetectionWithResult:result
+                                            timestampInMilliseconds:timeStampInMilliseconds
+                                                              error:callbackError];
+        });
       };
     }
 
@@ -112,6 +144,7 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
       return nil;
     }
   }
+
   return self;
 }
 
@@ -224,5 +257,4 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
   return [_visionTaskRunner processLiveStreamPacketMap:inputPacketMap.value() error:error];
 }
 
-
 @end

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetectorOptions.h

@@ -20,19 +20,70 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+@class MPPObjectDetector;
+
+/**
+ * This protocol defines an interface for the delegates of `MPPObjectDetector` object to receive
+ * results of performing asynchronous object detection on images (i.e, when `runningMode` =
+ * `MPPRunningModeLiveStream`).
+ *
+ * The delegate of `MPPObjectDetector` must adopt `MPPObjectDetectorLiveStreamDelegate` protocol.
+ * The methods in this protocol are optional.
+ */
+NS_SWIFT_NAME(ObjectDetectorLiveStreamDelegate)
+@protocol MPPObjectDetectorLiveStreamDelegate <NSObject>
+
+@optional
+
+/**
+ * This method notifies a delegate that the results of asynchronous object detection of
+ * an image submitted to the `MPPObjectDetector` is available.
+ *
+ * This method is called on a private serial dispatch queue created by the `MPPObjectDetector`
+ * for performing the asynchronous delegates calls.
+ *
+ * @param objectDetector The object detector which performed the object detection.
+ * This is useful to test equality when there are multiple instances of `MPPObjectDetector`.
+ * @param result The `MPPObjectDetectionResult` object that contains a list of detections, each
+ * detection has a bounding box that is expressed in the unrotated input frame of reference
+ * coordinates system, i.e. in `[0,image_width) x [0,image_height)`, which are the dimensions of the
+ * underlying image data.
+ * @param timestampInMilliseconds The timestamp (in milliseconds) which indicates when the input
+ * image was sent to the object detector.
+ * @param error An optional error parameter populated when there is an error in performing object
+ * detection on the input live stream image data.
+ *
+ */
+- (void)objectDetector:(MPPObjectDetector *)objectDetector
+    didFinishDetectionWithResult:(nullable MPPObjectDetectionResult *)result
+         timestampInMilliseconds:(NSInteger)timestampInMilliseconds
+                           error:(nullable NSError *)error
+    NS_SWIFT_NAME(objectDetector(_:didFinishDetection:timestampInMilliseconds:error:));
+@end
+
 /** Options for setting up a `MPPObjectDetector`. */
 NS_SWIFT_NAME(ObjectDetectorOptions)
 @interface MPPObjectDetectorOptions : MPPTaskOptions <NSCopying>
 
+/**
+ * Running mode of the object detector task. Defaults to `MPPRunningModeImage`.
+ * `MPPImageClassifier` can be created with one of the following running modes:
+ *  1. `MPPRunningModeImage`: The mode for performing object detection on single image inputs.
+ *  2. `MPPRunningModeVideo`: The mode for performing object detection on the decoded frames of a
+ *      video.
+ *  3. `MPPRunningModeLiveStream`: The mode for performing object detection on a live stream of
+ *      input data, such as from the camera.
+ */
 @property(nonatomic) MPPRunningMode runningMode;
 
 /**
- * The user-defined result callback for processing live stream data. The result callback should only
+ * An object that confirms to `MPPObjectDetectorLiveStreamDelegate` protocol. This object must
- * be specified when the running mode is set to the live stream mode.
+ * implement `objectDetector:didFinishDetectionWithResult:timestampInMilliseconds:error:` to receive
- * TODO: Add parameter `MPPImage` in the callback.
+ * the results of performing asynchronous object detection on images (i.e, when `runningMode` =
+ * `MPPRunningModeLiveStream`).
  */
-@property(nonatomic, copy) void (^completion)
+@property(nonatomic, weak, nullable) id<MPPObjectDetectorLiveStreamDelegate>
-    (MPPObjectDetectionResult *__nullable result, NSInteger timestampMs, NSError *error);
+    objectDetectorLiveStreamDelegate;
 
 /**
  * The locale to use for display names specified through the TFLite Model Metadata, if any. Defaults

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetectorOptions.m

@@ -33,7 +33,7 @@
   objectDetectorOptions.categoryDenylist = self.categoryDenylist;
   objectDetectorOptions.categoryAllowlist = self.categoryAllowlist;
   objectDetectorOptions.displayNamesLocale = self.displayNamesLocale;
-  objectDetectorOptions.completion = self.completion;
+  objectDetectorOptions.objectDetectorLiveStreamDelegate = self.objectDetectorLiveStreamDelegate;
 
   return objectDetectorOptions;
 }