A solution for video conference call embedded on website, SKYPE API?

Hello, Here is short description of our overall project: We’re building online tuition system and we going to incorporate one to one video call. We are looking for a solution to embed video conferencing software to our website. It can be SKYPE API/URI or any other software which would meet our requirements. Functionality requirements: Online status of each teacher Simple button on student’s web site to make video call with available teacher Screen sharing (important but not essential) High voice quality Scalability up to 5000 teachers and students talking at the time Call statistics log (student id, teacher id, time duration) Win/Mac availability, Mobile welcome but not essential We have not decide on what platform our website will be running so any solution is welcomed. Thank you for your attention! Regards, Jaro Kurimsky Technical director