Streaming Media - October 2008 - (Page 24)

tutorial Encoding for Screencams Table 1. Recommended Generic Encoding Settings Video Frame rate Data rate Bitrate control Constrained maximum I-frame settings Natural I-frames Audio Channels Bitrate control Rate Data rate Parameter 15 fps 250–400Kbps 2-pass variable bitrate Between 2x–4x of target data rate 10–20 seconds Enabled Mono Variable bitrate 22 kHz 32Kbps Figure 2. The WM Video V9 encoding controls from Sorenson Squeeze Table 1 contains a summary of these parameters for easy scanability. Now, let’s move to the codec-specific sections. Codec-Specific Findings One consistent lesson of streaming encoding is that different tools will produce varying levels of quality, even when using the same codec. This is especially true with H.264, where the four H.264-capable encoding tools represented in Table 2 use three different H.264 codecs, none of which, presumably, is fine-tuned for screencams, which represent a tiny percentage of streaming video. How did I choose the encoding tools? Premiere Pro and Final Cut Pro are obvious since many folks already own these tools. Note that I only gauged Final Cut Pro’s performance with H.264 because that’s the only codec that comes native with the program. I also wanted to include the homer encoding tools—Expression Encoder 2 for VC-1 and On2 Flix Pro for VP6—since these are produced by the codec vendor and should produce the best results. Sorenson Squeeze and Telestream Episode Pro are the two most popular and up-to-date batch encoding tools that cost less than $1,000, so I threw them into the mix as well. My goal with each codec was to produce the test file with each encoding tool, compare quality among them, note any outliers good or bad, and briefly discuss the codec-specific encoding parameters for each class. To save time, I focused mainly on getting a good result quickly, modifying default controls as minimally as possible to do so. As with all encoder comparisons, a poor score doesn’t necessarily mean that the encoding tool can’t produce high-quality video (though I did note some exceptions). Rather, it means that you may have to adjust some controls that I didn’t experiment with or simply encode at a higher data rate than you would with the higher rated tools. 24 STREAMING MEDIA October/November 2008 Figure 3. Make sure to enable natural keyframes where available. VP6 Encoding VP6 is a solid choice for Flash encoding, with very good quality and near-universal playback support. There are several wrinkles to consider with Flash encoding. First, note that there are now two techniques for VP6 encoding: VP6-S, which is simple to decode and, therefore, appropriate for high-definition, real-world video; and VP6-E, which offers excellent quality but may be harder to decode. If your encoding tool doesn’t offer a choice, you’re essentially producing VP6-E, which I used for all tests. Note that if you experience playback difficulties on lower-power computers, you should try VP6-S, which isn’t available on all tools. I produced a VP6-S file with Sorenson Squeeze and found it visually identical to the VP6-E file but slightly easier to decode (about 15% easier on an HP 8710p notebook computer, which is powered by a 2.2 GHz Core 2 Duo). Table 2. Summary of Encoding Quality Flash Adobe Premiere Pro Apple Compressor Microsoft Expression Encoder 2 On2 Flix Pro Sorenson Squeeze Telestream Episode Pro Avoid N/A N/A Very Good Very Good Very Good H.264 Poor Poor N/A N/A Very Good Fair VC-1 Poor N/A Fair N/A Very Good Fair

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Streaming Media - October 2008 Table of Contents Standard Time Technology and Business Trends by the Numbers Encoding for Screencams Meeting the Enterprise Video Distribution Challenge Pulling Back the Curtain on Level 3 The 2008 Streaming Media Readers’ Choice Award Winners The Ultimate Guide to Creating Online Video Content That Works, Part 1 Brave New Platforms Video From the Democratic National Convention—Both Official and Unofficial—Made Clear That It’s No Longer Politics as Usual Creative Suite Turns 4 The Future of Internet Radio Decoding the Truth About Hi-Def Video Production Educating the Next Generation of Online Media Makers ViewCast Niagara GoStream SURF The Past and Future of Online Video: I’m Not Dead Yet!

Streaming Media - October 2008

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