h264 bitrate exceed my value in runtime

[Amirhos-esm]

hello I am using this Configuration for my encoder.

VencH264Param h264ParamDefualt = { .bEntropyCodingCABAC = 1, .nBitrate = 1 * 1024 * 1024, .nFramerate = fps, .nCodingMode = VENC_FRAME_CODING, .nMaxKeyInterval = fps, .sProfileLevel.nProfile = VENC_H264ProfileMain, .sProfileLevel.nLevel = VENC_H264Level31, .sQPRange.nMinqp = 10, .sQPRange.nMaxqp = 32, };

but I wondering why bitrate exceed 1 * 1024 * 1024