Originally Posted by Rich127
The 24 Mbps does not seem to be a great improvement over 17 Mbps as so many have predicted....
I've played around with my Canon HG20, and I concur with that assessment. The optical-section of the camera doesn't really perform all the way out to 1920x1080. At the full-zoom (12x) end of the lens, there's substantial chromatic aberration (CA), giving white contrasty-objects an ugly purplish halo. The lens seems to perform best in the mid-range -- minimal CA and just a tad sharper than the two extremes of wide/zoom. IMHO, 1440x1080 (@ 17Mbps) was a sensible compromise in the HG10.
In daylight scenes with limited subject motion and no panning, I can see no appreciable difference between 17Mbps and 24Mbps. Here, 24Mbps is just a waste of bits. Perhaps if the camcorder-optics were higher-quality, we could extract more detail, but that's not realistic for a consumer-grade cam (where a bigger zoom-range is more useful to more people.)
In daylight 'busy scenes', under frame-by-frame analysis on a PC monitor, I can see an improvement with 24Mbps. The motion-disturbed area start to show macroblocking artifacts (depending on the amount of 'change' between the previous and current frames.) And at those hotspots, the higher-bitrate video consistently suffers fewer motion artifacts. So the extra bits are doing something useful.
However, I should point out, when I watched my testclips or a regular HDTV, at normal (1x) speed, the differences weren't perceptible to me. Perhaps a professional with a trained eye could reliably identify the better video, but not me! No doubt there are creative shots where 24Mbps offers a clear and obvious improvement (for example, a panning shot through a chain-link fence.) As I said earlier, the bitrate isn't the bottleneck, it's the HG20's camera-optics. (That's probably true for most of today's HD-camcorders.)
In low-light scenes, video-noise dominates the compression-engine. Ironically, 24Mbps once again offers a noticeable improvement, mainly because random video-noise is hard to compress, and a lot of bits are wasted on those random dots. 24Mbps has better 'grain retention', which is another way of saying, it does a better at faithfully capturing the limitations of the CMOS sensor (without adding a lot of macroblocking effects.)