use Service or use Native Activity with android camera app

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hi,All

I am working unity3d run at android with camera app. I have no more with java and NDK, I have experence with C++ and unity3D. I want to write a service at background to detect motion with camera, and this plugin will invoke by Unity3D, here comes question, I look through SDK here has two choose . 1 : use opencv manager like sample Color Blob Detection,I change it into a android service , and send data to unity3D. I think this will be recommended for flexible and follow android framework. 2 : use Native Activity as sample, deal all process at C++ , and return data to unity3D. I think this will get more performance.

I don't now which is good , or better solution? any suggestion will be great appreciated.