Building NBCOlympics.com with Silverlight

The multi-bitrate content that's adaptively streamed is all pre-encoded, so the server isn't doing any "resampling" on the fly. The other big difference about adaptive streaming from the way live streams are being delivered, and Eric talks about this in the video, is that adaptive streaming is done using regular HTTP downloads from regular HTTP servers. Windows Media Services isn't involved in adaptive streaming at all. The adaptive video streams are delivered as a series of small files, which the Olympics player then concatenates into a single, uninterrupted stream. It's during this process that the player can decide whether to fetch bigger (higher quality) or smaller (lower quality) chunks to match the user's bandwidth.

Encoding resolution and bitrate are related in this case. The lower the bitrate - the lower the resolution. This is done in order to work around an inherent property of compressed digital video - macroblocking. Because VC-1 video is compressed in 16x16 macroblocks, insufficient bitrate for a given resolution can lead to obvious blocking artifacts in decoded video. The easiest way to avoid this is to lower the resolution whenever the bitrate is deemed insufficient to produce "block-free" video. It's still nearly impossible to entirely avoid blocking (after all, not all video is equally complex - just compare swimming action to chess action), but changing the resolution proportionally to the bitrate helps minimize it.