无法从CGRect值中检索正确的AVMetadataItem

Question

我将CGRect值存储在AVTimedMetadataGroups中，作为视频文件中的AVAssetTrack。当使用元数据读取文件时，我无法成功地提取原始CGRect值。到目前为止，我的情况如下：

编写代码：

    AVMutableMetadataItem *roiItem = [AVMutableMetadataItem metadataItem];
    roiItem.identifier = ID_ROI;
    roiItem.dataType = (__bridge NSString *)kCMMetadataBaseDataType_RectF32;
    roiItem.value = [NSValue valueWithCGRect:videoFrame.roi];

    CMTime frameEndTime = CMTimeAdd(videoFrame.timestamp, _frameDuration);

    AVTimedMetadataGroup *metadataGroup = [[AVTimedMetadataGroup alloc] initWithItems:@[roiItem] timeRange:CMTimeRangeMake(videoFrame.timestamp, frameEndTime)];
    while (_avAssetWriterInputMetaData.readyForMoreMediaData == NO) {
        NSDate *maxDate = [NSDate dateWithTimeIntervalSinceNow:0.1];
        [[NSRunLoop currentRunLoop] runUntilDate:maxDate];
    }
    BOOL isMetaOK = [_avAssetWriterMetadataAdaptor appendTimedMetadataGroup:metadataGroup];
    if (! isMetaOK) {
        NSLog(@"[VideoCamera.writeVideoFrame]: Error writing ROI metadata");
    }

读“守则”：

    if ( [metadataItem.dataType isEqualToString:(NSString *) (__bridge NSString *)kCMMetadataBaseDataType_RectF32] &&
         [metadataItem.identifier isEqualToString:ID_ROI] ) {

        NSLog(@"metadataItem value %@ class %@", metadataItem.value, [metadataItem.value class]);

        NSObject *rawObject = metadataItem.value;

        NSValue *aValue = [NSValue valueWithBytes:&rawObject objCType:@encode(CGRect)];

        NSLog(@"aValue: %@", aValue);

        NSValue *bValue = [NSValue valueWithNonretainedObject:metadataItem.value];

        NSLog(@"bValue: %@", bValue);

        roi = [bValue CGRectValue];

        NSLog(@"roi: %f %f %f %f", roi.origin.x, roi.origin.y, roi.size.width, roi.size.height);

        break;
    }

控制台输出：

2015-10-27 14:22:36.010 xctest[18953:363781] metadataItem value NSRect: {{722.97998046875, 16.460000991821289}, {299.04000854492188, 224.27999877929688}} class NSConcreteValue
2015-10-27 14:22:36.010 xctest[18953:363781] aValue: NSRect: {{6.9457258969245994e-310, 9.2737718544569335e-316}, {2.1742214229791141e-314, nan}}
2015-10-27 14:22:36.011 xctest[18953:363781] bValue: <d02c300b dc7f0000>

任何线索都被欣赏了。

XCode7，IOS9

Answer 1

在您的读取代码中，尝试如下：

CGRect roi = ((NSValue *)metadataItem.value).CGRectValue;