[camera]fix a sample buffer memory leak on pause resume recording (flutter#5927)

This memory leak happens when pause/resume the recording. Depending on camera resolution, about 1-2MB leaks for every resume, so it can add up pretty fast if we frequently pause/resume. 

We only reference this sample buffer inside the scope of this method (e.g. directly piping into file IO), so no need to retain it again, as it's already retained and will be released afterwards by apple. (We did keep around the pixel buffer, but we already manually [retain](https://github.com/flutter/packages/blob/d7ee75ad59ad7bc45e659d0599e935e9e7981ea1/packages/camera/camera_avfoundation/ios/Classes/FLTCam.m#L403) and [release](https://github.com/flutter/packages/blob/d7ee75ad59ad7bc45e659d0599e935e9e7981ea1/packages/camera/camera_avfoundation/ios/Classes/FLTCam.m#L415) that)

Bug was introduced in flutter/plugins#1370. 

*List which issues are fixed by this PR. You must list at least one issue.*

flutter#132013

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

Author: hellohuanlin

packages/camera/camera_avfoundation/CHANGELOG.md

@@ -1,6 +1,7 @@
-## NEXT
+## 0.9.13+11
 
-* Remove development team from example app.
+* Fixes a memory leak of sample buffer when pause and resume the video recording.
+* Removes development team from example app.
 * Updates minimum iOS version to 12.0 and minimum Flutter version to 3.16.6.
 
 ## 0.9.13+10

packages/camera/camera_avfoundation/example/ios/RunnerTests/FLTCamSampleBufferTests.m

@@ -38,6 +38,41 @@ - (void)testCopyPixelBuffer {
   CFRelease(deliveriedPixelBuffer);
 }
 
+- (void)testDidOutputSampleBuffer_mustNotChangeSampleBufferRetainCountAfterPauseResumeRecording {
+  FLTCam *cam = FLTCreateCamWithCaptureSessionQueue(dispatch_queue_create("test", NULL));
+  CMSampleBufferRef sampleBuffer = FLTCreateTestSampleBuffer();
+
+  id writerMock = OCMClassMock([AVAssetWriter class]);
+  OCMStub([writerMock alloc]).andReturn(writerMock);
+  OCMStub([writerMock initWithURL:OCMOCK_ANY fileType:OCMOCK_ANY error:[OCMArg setTo:nil]])
+      .andReturn(writerMock);
+  __block AVAssetWriterStatus status = AVAssetWriterStatusUnknown;
+  OCMStub([writerMock startWriting]).andDo(^(NSInvocation *invocation) {
+    status = AVAssetWriterStatusWriting;
+  });
+  OCMStub([writerMock status]).andDo(^(NSInvocation *invocation) {
+    [invocation setReturnValue:&status];
+  });
+
+  FLTThreadSafeFlutterResult *result =
+      [[FLTThreadSafeFlutterResult alloc] initWithResult:^(id result){
+          // no-op
+      }];
+
+  // Pause then resume the recording.
+  [cam startVideoRecordingWithResult:result];
+  [cam pauseVideoRecordingWithResult:result];
+  [cam resumeVideoRecordingWithResult:result];
+
+  [cam captureOutput:cam.captureVideoOutput
+      didOutputSampleBuffer:sampleBuffer
+             fromConnection:OCMClassMock([AVCaptureConnection class])];
+  XCTAssertEqual(CFGetRetainCount(sampleBuffer), 1,
+                 @"didOutputSampleBuffer must not change the sample buffer retain count after "
+                 @"pause resume recording.");
+  CFRelease(sampleBuffer);
+}
+
 - (void)testDidOutputSampleBufferIgnoreAudioSamplesBeforeVideoSamples {
   FLTCam *cam = FLTCreateCamWithCaptureSessionQueue(dispatch_queue_create("testing", NULL));
   CMSampleBufferRef videoSample = FLTCreateTestSampleBuffer();

packages/camera/camera_avfoundation/ios/Classes/FLTCam.m

@@ -514,7 +514,6 @@ - (void)captureOutput:(AVCaptureOutput *)output
       return;
     }
 
-    CFRetain(sampleBuffer);
     CMTime currentSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
 
     if (_videoWriter.status != AVAssetWriterStatusWriting) {
@@ -564,18 +563,18 @@ - (void)captureOutput:(AVCaptureOutput *)output
       _lastAudioSampleTime = currentSampleTime;
 
       if (_audioTimeOffset.value != 0) {
-        CFRelease(sampleBuffer);
-        sampleBuffer = [self adjustTime:sampleBuffer by:_audioTimeOffset];
+        CMSampleBufferRef adjustedSampleBuffer =
+            [self copySampleBufferWithAdjustedTime:sampleBuffer by:_audioTimeOffset];
+        [self newAudioSample:adjustedSampleBuffer];
+        CFRelease(adjustedSampleBuffer);
+      } else {
+        [self newAudioSample:sampleBuffer];
       }
-
-      [self newAudioSample:sampleBuffer];
     }
-
-    CFRelease(sampleBuffer);
   }
 }
 
-- (CMSampleBufferRef)adjustTime:(CMSampleBufferRef)sample by:(CMTime)offset CF_RETURNS_RETAINED {
+- (CMSampleBufferRef)copySampleBufferWithAdjustedTime:(CMSampleBufferRef)sample by:(CMTime)offset {
   CMItemCount count;
   CMSampleBufferGetSampleTimingInfoArray(sample, 0, nil, &count);
   CMSampleTimingInfo *pInfo = malloc(sizeof(CMSampleTimingInfo) * count);

packages/camera/camera_avfoundation/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera_avfoundation
 description: iOS implementation of the camera plugin.
 repository: https://github.com/flutter/packages/tree/main/packages/camera/camera_avfoundation
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.9.13+10
+version: 0.9.13+11
 
 environment:
   sdk: ^3.2.3