Keep in mind that HD and HQ are totally different things. The original poster is asking about HQ, not HD.
"HQ" videos on YouTube are actually Quicktime mp4 files. A lot of people don't understand or even believe this. But it is 100% true, YouTube's player plays .mp4. When videos are uploaded to YouTube, they are converted to both .flv and .mp4. If a video does not have the "HQ" button, you can append "&fmt=18" (without the quotes) to the URL to play the .mp4 version.
I'm not sure if Replay Media Catcher handles Quicktime properly or not.
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