Do I fulfill the Mitzva of ViShinantam, i.e.Talmud Torah, every time someone goes onto the site and hears an audio tape of a shiur I gave? And if so, if I had to chose between giving a shiur to three participants or using the time to record a shiur that will be heard by many people, should I give priority to recording the shiur (even though no one is listening to the shiur until the shiur is uploaded onto an internet site)?
Placing a shiur on the Internet is an act of teaching Torah, passing on the Torah knowledge to others.
The mitzvah is not performed each time somebody listens to the shiur, yet when other listen to the shiur the mitzvah of teaching Torah – which was fulfilled in uploading the shiur to the Internet – gets “bigger” – in uploading the shiur you will have taught Torah to more people.
The question of an Internet shiur verses a real-life shiur is not a technical matter of VeShinantam but rather a question of quality versus quantity. It stands to reason that the quality of teaching is higher when people are actually present, yet the quantity is greater on the Internet. When both cannot be done one would have to weigh up one against the other (depending also on how many Talmidim the Internet will provide) and reach a decision.