A computer implemented method for optimizing transmission of streaming video contents based on user Quality-of-Experience, QoE, metrics, the streaming video contents being transmitted from a video hosting server to a video player on a terminal over a network connection, the method comprises receiving (101,201), at an optimization module and from at least one video player communicatively coupled to the optimization module, at least one QoE metric related to a particular video stream; analysing (102,202), by the optimization module, the at least one QoE metric with respect to at least one QoE policy associated to the at least one QoE to optimize the transmission of the particular video stream; characterised in that the method further comprises: determining (103,203), by the optimization module, adjustments in operative parameters of an application layer between the video hosting server and the video player in the transmission of the particular video stream based on the analysis; notifying the adjustments to corresponding participants on the video streaming content delivery pipeline controlling the application layer in the transmission of the particular video stream, the participants being video content providers, video content publishers, video content distributors, video content service providers, video encoding/streaming technology providers or media player's Internet Service Providers; and causing, by the optimization module, the adjustments to be applied in the application layer across the participants on the video streaming content delivery pipeline. receiving (101,201), at an optimization module and from at least one video player communicatively coupled to the optimization module, at least one QoE metric related to a particular video stream; analysing (102,202), by the optimization module, the at least one QoE metric with respect to at least one QoE policy associated to the at least one QoE to optimize the transmission of the particular video stream; characterised in that the method further comprises: determining (103,203), by the optimization module, adjustments in operative parameters of an application layer between the video hosting server and the video player in the transmission of the particular video stream based on the analysis; notifying the adjustments to corresponding participants on the video streaming content delivery pipeline controlling the application layer in the transmission of the particular video stream, the participants being video content providers, video content publishers, video content distributors, video content service providers, video encoding/streaming technology providers or media player's Internet Service Providers; and causing, by the optimization module, the adjustments to be applied in the application layer across the participants on the video streaming content delivery pipeline. determining (103,203), by the optimization module, adjustments in operative parameters of an application layer between the video hosting server and the video player in the transmission of the particular video stream based on the analysis; notifying the adjustments to corresponding participants on the video streaming content delivery pipeline controlling the application layer in the transmission of the particular video stream, the participants being video content providers, video content publishers, video content distributors, video content service providers, video encoding/streaming technology providers or media player's Internet Service Providers; and causing, by the optimization module, the adjustments to be applied in the application layer across the participants on the video streaming content delivery pipeline.