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MillimeterEncoding Best Practices, Part 2
Jun 23, 2008 12:00 PM, By Jan Ozer
Table 2. HD video quality by codec
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HD Tests
I produced all HD test files at 1280x720 at 30fps, with a data rate of 800kbps for video and 128kbps for audio. These rates are insanely aggressive, but I started at 1500kbps and kept reducing the data rate until all the codecs started exhibiting some flaws. I produced using two-pass variable-bit-rate encoding (VBR) at the highest supported profile for H.264 and using VC-1 parameters again supplied by Microsoft’s Waggoner. With Flix Pro, I set all quality settings for VP6 at the highest supported levels. Table 2 shows the results.
Figure 4. VC-1 exhibits much lower quality than the other contenders in this easy-to-compress clip.
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Still-image tests revealed a couple of surprises. First, as shown in Figure 4, VC-1 had trouble maintaining quality even with low-motion clips such as a talking head. Not only did VC-1 lose detail, the clip lost color saturation and shows artifacts not present in any other clip.
Second surprise: the clip compressed with the On2's newly updated VP6 codec showed substantially greater detail retention than the VP6-S clip that I officially tested, which looks slightly fuzzy. Both trends are even more evident in the much harder-to-compress Figure 5, where the VC-1 clip is noticeably more degraded as compared with the other three frames, and where the "New VP6" clip preserves more detail than the VP6-S clip. In all comparisons, H.264 exhibited the best still frame quality.
Figure 5. This high-motion test clip makes On2's new version of its VP6 codec look very promising (but does nothing to dispel concerns about Microsoft's VC-1).
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H.264’s advantage over VP6 was reversed during realtime playback tests, where VP6 proved quieter than H.264. Surprisingly, given its stellar performance in SD tests, VC-1 was much noisier during realtime playback than either other codec, probably because of the still frame artifacts seen in Figures 4 and 5. None of the codecs dropped frames in these tests, so smoothness scores were equal.
Overall, as you can see in Table 2, VP6 and H.264 tied for HD quality, with VC-1 last. Note that these results are consistent with past comparisons, where WMV/VC-1 has ranked last in all three tests that I’ve performed since 2005. Again, this doesn’t mean that you can’t produce high-quality HD files with VC-1. Rather, it means that you’ll probably need to encode at a 10-percent to 20-percent higher data rate to produce the same quality as H.264.
Keeping all this in mind, few producers choose a codec solely based on quality. That said, it’s obviously always an important consideration and I hope you find this information useful.
