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The term P2PTV refers to peer-to-peer (P2P) software applications designed to redistribute video streams in real time on a P2P network; the distributed video streams are typically TV channels from all over the world but may also come from other sources. The draw to these applications is significant because they have the potential to make any TV channel globally available by any individual feeding the stream into the network where each peer joining to watch the video is a relay to other peer viewers, allowing a scalable distribution among a large audience with no incremental cost for the source. ==Technology and use== In a P2PTV system, each user, while downloading a video stream, is simultaneously also uploading that stream to other users, thus contributing to the overall available bandwidth. The arriving streams are typically a few minutes time-delayed compared to the original sources. The video quality of the channels usually depends on how many users are watching; the video quality is better if there are more users. The architecture of many P2PTV networks can be thought of as real-time versions of BitTorrent: if a user wishes to view a certain channel, the P2PTV software contacts a "tracker server" for that channel in order to obtain addresses of peers who distribute that channel; it then contacts these peers to receive the feed. The tracker records the user's address, so that it can be given to other users who wish to view the same channel. In effect, this creates an overlay network on top of the regular internet for the distribution of real-time video content. The need for a tracker can also be eliminated by the use of distributed hash table technology. Some applications allow users to broadcast their own streams, whether self-produced, obtained from a video file, or through a TV tuner card or video capture card. Lots of the commercial P2PTV applications were developed in China (TVUPlayer, PPLive, QQLive, PPStream). The majority of available applications broadcast mainly Asian TV stations, with the exception of TVUPlayer, which carries a number of North American stations including CBS, Spike TV, and Fox News. Some applications distribute TV channels without a legal license to do so; this utilization of P2P technology is particularly popular to view channels that are either not available locally, or only available by paid subscription, as is the case for some sports channels. Distributing links to pirated P2PTV feeds on a U.S.-based Web site can result in the U.S. government seizing the Web site, as it did with several P2PTV aggregation sites prior to Super Bowl XLV.〔Martinez, Jennifer (2011-02-02). (Feds seize sports websites before Super Bowl ). ''The Politico''. Retrieved 2011-02-02.〕 By January 2009, there were about 14,000 P2P channels on PPStream. Other commercial P2PTV applications outside China are Abroadcasting (USA), Zattoo (Switzerland/USA), Octoshape (Denmark), LiveStation (UK). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「P2PTV」の詳細全文を読む スポンサード リンク
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