How can i configure reference frames in AVAssetWriter, using H264?

Question

I'm trying to write a mp4 using AVFoundation and AVAssetWriter.

I'm configuring my compression as follows:

    NSDictionary* compressionSettings   = @{ AVVideoAverageBitRateKey : @(1048576),
                                             AVVideoMaxKeyFrameIntervalKey : @(12),
                                             AVVideoProfileLevelKey : AVVideoProfileLevelH264HighAutoLevel,
                                             (NSString*)kVTCompressionPropertyKey_AllowFrameReordering : @(NO),
                                             (NSString*)kVTCompressionPropertyKey_H264EntropyMode : (NSString*)kVTH264EntropyMode_CAVLC
                                           };

    AVAssetWriterInput* videoInput      = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:outputSettings];

While this is working great - when I analyze the file it tells me, that the entropy is using 2 reference frames, where I need only one.

None of the keys that are available in AVVideoSettings.h or VTVideoCompressionProperties.h seem to do the trick.

Is there a way to configure the AVAssetWriterInput in such a way, that the H.264 stream will only use 1 reference frame?