roslibjs audio_common_msgs wrong array length

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Hi,

I publish audio_common_msgs Audiodata from my ros module and subscribe to it via roslibjs

    var audio_topic = new ROSLIB.Topic({
    ros : ros,
    name : '/camera/audio',
    messageType : 'audio_common_msgs/AudioData'
});

It works but the length of the data is incorrect. I send predefined array sizes of 512 and check in my ros module if the length is really 512. However in my roslibjs webpage the data is of length 684. I dont know where the other array values come from. Can someone help me out?

thanks