I want to increase the zip compression rate of video files in Unity.

We have created a zip compression process using GZipStream.

The following code is used to compress the video file (mp4) stored in the terminal, but the compression rate is 98 to 99 percent, and the purpose of reducing the capacity is not achieved.

I would appreciate it if you could tell me about the library that can be highly compressed with Unity and the code modifications.
Thank you for your cooperation.

environment:
Unity 2018.4.22.f1

created code:

public static byte[] Compress (byte[] src)
{
    using(varms=new MemoryStream())
    {
        using(vards=new GZipStream(ms, CompressionMode.Compress, true/*ms is */))
        {
            ds.Write(src,0,src.Length);
        }
        ms.Position = 0;
        byte [ ] comp = new byte [ms.Length];
        ms.Read(comp,0,comp.Length);
        return comp;
    }
}