Multimedia adaptation aims at matching video quality to user needs and device restrictions. This technique has a high computational cost, specially when working with video transcoding, being necessary to estimate it during the de- sign of architectures and applications. This paper presents an analytical model to quantify these video transcoding costs in a hardware independent way. The model was used to analyze the impact of transcoding delays in end-to-end live-video transmissions over LANs, MANs and WANs. Two different transcoding architectures were considered: a se- quential and a parallel. The experiments conduced allow to indicate the best one for different scenarios.