The BitTorrent protocol is by far the most popular protocol for offline peer-to-peer video distribution on the Internet. BitTorrent has previously been extended to support the streaming of recorded video, that is, Video-on-Demand (VoD). In this paper, we take this support for video streaming a step further by presenting extensions to BitTorrent for supporting live video streaming, which we have implemented in our BitTorrent client called Tribler. We have tested our extensions both by running simulations, and by deploying our implementation in a public trial in the Internet, using the optimal values of several parameters as found in the simulations. We analyse the performance of Tribler in systems with varying values for the percentage of peers behind a firewall or NAT, which we consider to be one of the key parameters in the performance of deployed P2P systems. Our public trial lasted 9 days, during which 4555 unique peers participated from around the globe. We found 61% of the peers to be behind a firewall, a level at which our simulations still indicate acceptable performance. Most of the peers indeed obtained good performance, with for instance a very low prebuffering time before playback starts, indicating the feasibility of our approach. The median prebuffering time we measured was 3.6 seconds, which is 3–10 times shorter than the prebuffering time measured in other deployed peer-to-peer systems.