I am currently following OpenCon2015 online and really enjoying the experience.
There are two main components: A YouTube live feed and a Twitter feed (#opencon). The Twitter feed and the high number of live Tweets is really what makes this work! You not only watch the talk about you also "hear" the thoughts of the audience (both the "live" and "feed" audience) and you can interact with these people live (and follow up on discussions afterwards). This makes you really feel like you're there and not sitting on the couch in your living room.
To make this work in practice it appears that you need
1. A camera and someone operating it (zooming/panning)
2. A sound system linked to the camera, a microphone for the speaker and 1-2 rowing mikes for questions.
3. A camera/computer interface for the live feed and reasonably fast internet
4. Some basic html skills to make the live feed page, i.e. embed the YouTube feed and Twitter feed side-by-side. (I found it quite important to be able to view the two simultaneously).
5. Lots of people live Tweeting
I really hope that these talks also will be available for later viewing!
Anyway, if more scientific meetings and conferences would adopt this model it would greatly improve their impact and further science as a whole.
Also, for smaller meetings the streaming could probably be done with a smartphone and Periscope.
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