The heterogeneous structure of the Internet is a great obstacle for establishing real-time video services. Scalable video codecs, generating bit-streams decodable at di erent rates, have been proposed to address the heterogeneity problem. In this paper, we will review standardcompliant and non-compliant codec architectures for Internet video-ondemand. For compression based on the H.263 standard, we h a ve developed a compatible architecture that allows to switch b e t ween preencoded

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... of di erent bit-rates. This architecture provides excellent streaming performance for point-to-point communication scenarios that o er a low delay feedback c hannel. Then we present a non-compliant fully scalable video codec based on a spatio-temporal resolution pyramid that is available as a Netscape plugin for the World Wide Web. This approach can encode embedded lower bit-rate layers at the same overall bit-rate as needed by H.263 single-layer coding and can also support multicasting. Finally, w e show h o w scalable video coding can be e ciently combined with a retransmission protocol achieving graceful degradation and investigate the streaming performance of the above architectures.