OTT(Over The Top)屬於開放式網路環境，缺乏完善的頻寬管理機制，因此容易在傳輸數位影音內容時受到網路傳輸頻寬不足或可用頻寬不穩定及傳輸品質因素等影響，造成使用者在觀賞多媒體影音內容時出現畫面暫停或是殘影等現象。目前pull-based OTT影音串流服務主要使用兩種方式，漸進式下載(Progressive Download)，例如Youtube，另一種為可適性串流(Adaptive Streaming)，例如Microsoft Smooth Streaming，作為傳遞影音內容的方式，此兩種方式都有其缺點。本論文提出基於事件觸發之可適性串流技術 - Event-driven Adaptive Streaming (EDAS)，在EDAS方法中，伺服器端透過TCP傳輸協定傳送影片，傳送速率不是由伺服器端控制，而是由TCP本身的流量控制機制調整，以達到充分的利用可用頻寬，同時用戶端以事件觸發的方式依可用頻寬預測，及緩衝器狀態觸動HTTP協定改變下載內容，讓用戶達到當下可利用頻寬之最佳觀看品質，並能大量減少伺服器端需要處理的請求。

OTT(Over The Top) is operated in unmanaged network environments, which do not deployed bandwidth and QoS management mechanisms. Because of the limitation and the dynamic changing of available bandwidth in this kind of networks, OTT should provide a mechanism to adapt the network dynamic. Traditionally, there are two major methods for pull-based streaming services like OTT. One is Progressive Download represented by Youtube and the other is Adaptive Streaming represented by Microsoft Smooth Streaming. Both of them have their shortage in adapting to network dynamic and usage of available bandwidth. In this paper, we proposed an Event-Driven Adaptive Streaming (EDAS) mechanism. In our scheme, the aggressive transmission is used by the server to fully unitize the available bandwidth to transfers the stream data to receivers. On the other hand, the receiver should trigger the HTTP requests to change the download streaming quality by events with the estimation of the available bandwidth and the status of media buffer. It can also reduce a large number of requests that the server should handle.