Streaming Media - August/September 2008 - (Page 30)

tutorial High-Touch Encoding With Expression Encoder 2 they contain the important visual data of the faces on the cards, so we want them to be as high quality as possible. DQuant spends too many bits on smooth parts of the image to use on every frame, but upping the bitrates on a few dozen I-frames won’t hurt overall quality much, and it improves the quality of the static parts of the card we wind up staring at for those many seconds. FILTERS Figure 7. I output the job to the Silverlight Streaming Service. • In-Loop: On—In-Loop should always be on unless using Simple Profile; it helps reduce artifacts and improves quality (particularly at these aggressive bitrates) with no real downside. • Overlap: On—The Overlap filter further hides artifacts, which are a challenge with motion graphics at such a low bitrate. It can reduce detail a bit at higher bitrates, but that’s not the scenario here. • Denoise: Off—The source doesn’t have a hint of noise. If there are a lot of textures, Denoise can help to soften them some for easier encoding, but there’s not much texture here, either. • Noise Edge Removal: Off—This is really only useful for noisy edges of analog captures, and even then we’re better off cropping. It obviously doesn’t apply here. GROUP OF PICTURES • B-Frame Number: 2—This sets the number of consecutive B-frames between I- and P-frames in the encode. Normally we’d use one for film and video sources, but for these kinds of motion graphics two is more efficient. This gives us an IBBP pattern, so each B-frame is adjacent to an I- or P-frame. Three B-frames is less efficient in this case, since with the IBBBP pattern the middle B-frame is two frames away from a reference frame (only I- and P-frames can be reference frames), and the P-frames are too far apart, so they require more bits to store the change over four frames instead of three since the previous I- or P-frame. Since the worst-case latency for random access is determined by the maximum number of P-frames per GOP, increasing the number of B-frames will improve latency at a given GOP size. With 15 seconds between keyframes at 30 fps, two B-frames gives us the same random access latency as 5 seconds without B-frames (the old Windows Media Encoder default). • Scene Change Detection: On—This will give us natural keyframes where needed. The codec seems to do a good job of putting them in the right place. I’ve never changed this in Expression Encoder. • Adaptive GOP: On—Adaptive GOP allows the length of a GOP to vary with content. Always have this on. • Closed GOP: Off—This is required to be on for CBR encodes in Expression, but it slightly reduces the quality with VBR encoding. In particular, it can increase keyframe popping, since an Open GOP pattern starts with B-frames before the first keyframe or I-frame. You get BBIBBPBBP and so on, with the B-frames able to reference the last P-frame of the previous Figure 8 (far left). A VP6 frame following a transition Figure 9 (near left). The same frame as shown in Figure 8 after it’s been encoded in VC-1 30 STREAMING MEDIA August/September 2008

Table of Contents Feed for the Digital Edition of Streaming Media - August/September 2008

Streaming Media - August/September 2008 Table of Contents No Doubt - Editor's Note Mo’ Videos, Mo’ Money: Solving the Problem of Network Cost Why Good Design Matters More Than Ever: Just. Press. Play. Technology and Business Trends by the Numbers High-Touch Encoding With Microsoft Expression Encoder 2 The State of the Content Delivery Market, 2008 Get a Life: New Tools Put Lifecasting Within Anyone’s Reach So Many Codecs, So Little Time: Comparing H.264 Files Using Codecs From Apple, Dicas, and MainConcept Writing an RFP for Maximum ROI: Things to Consider and Questions to Ask When Writing a Request for Proposal for a Corporate Webcasting System The Patent Wars Producing Screencams in Camtasia Studio Analyze That Using Video to Communicate Change for Business Success Intellectuals’ Property Rights

Streaming Media - August/September 2008

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