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MillimeterEncoding Best Practices, Part 1
Jun 9, 2008 12:00 PM, By Jan Ozer
Table 4. Data rate at given frame rates.
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Frame Rate
Next, I wanted to determine how the frame rate used by the various entities impacted the data rate. In theory, one reason to use 15fps as opposed to 30fps would be the ability to drop the data rate. Certainly this is true in the corporate space, where those producing at 15fps used a data rate 89 percent lower than those producing at 30fps.
In the Broadcast – Midrange group, which was the only broadcast group with a meaningful sampling of 15ftp and 30fps producers, the difference wasn’t quite that stark. Those producing at 15fps used an average data rate of 25 percent less than those producing at 30fps.
Interestingly, however, those producing at 24fps used a lower data rate than 15fps producers. If you have the option to shoot at 24fps, this may be a technique that allows you to drop the data rate while retaining both smoothness and visual frame quality. Note, however, that all producers in the Broadcast – Aggressive group produced at 30fps.
Table 5. Audio data rates for Flash and Windows Media Audio.
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Audio Data Rate
The final parameter I reviewed was audio data rate, looking at two specific items. First, many producers use 128kbps audio just because it’s a default in many templates. Clearly, if the Broadcast – Midrange group thinks that 66kbps is fine for Flash and 48kbps fine for Windows Media Audio, it’s probably sufficient for most producers.
I separated these stats out by Flash and Windows Media to highlight the fact that the MP3 codec used in Flash is less efficient than either Windows Media Audio or the AAC audio codec included in H.264. In fact, some broadcast producers still using Windows Media, such as Sports Illustrated, broadcast at 32kbps. If you’re planning on switching from Windows Media to Flash, you'd better count on bumping the same data rate to produce the same quality.
That's it for this issue. Check back next time for a comparison of H.264, VC-1, and VP6 codecs using SD, HD, and screencam videos.
Continue the discussion on “Crosstalk” the Millimeter Forum.