Get bitrate from m4a file

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C#

C#4.0

Hello, how can I get bitrate from m4a file?

What I have tried:

Now I use - TAG Lib.. but he does not return my bitrate

Here is the Code:

TagLib.File AudioInfo = TagLib.File.Create(Input);

Bitrate = AudioInfo.Properties.AudioBitrate;
AudioChannels = AudioInfo.Properties.AudioChannels;
Freequency = AudioInfo.Properties.AudioSampleRate;

AudioInfo.Dispose();

He returns everything except bitrate..