Futuremark paper has more info about specific benchmarks and they write this:

Video transcoding
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Video transcoding workloads transcode videos by changing the resolution, framerate and bitrate of the video. Video transcoding uses Fast Transcode feature found in Windows 7 Media Foundation.

Video downscaling workload (found in Entertainment and PCMark tests) source video is H.264 (1080p, 30fps, 12Mbps). The destination is H.264 (320x240, 30fps, 500kbps).

High quality video transcoding workload (found in Creativity test) source video is the same as with downscaling workload. The destination is H.264 (1080p, 24fps, 10Mbps).

http://www.pcmark.com/wp-content/upl...Whitepaper.pdf

So, it was not truly synthetic code from labs of Intel, AMD or Nvidia. Now developers can create or modify their apps to use MS media transcode library along with enhanced AMD FX utilization in Windows 8.