Streaming Media - August/September 2008 - (Page 28)

tutorial High-Touch Encoding With Expression Encoder 2 reducing popping issues. The Silverlight version still would have looked a lot better than the original Flash even if I hadn’t set them, but the markers did provide a further boost in quality (Figure 4). But don’t think this is something that should be done for all clips; this clip is unusual in having minutes without cuts with a mix of static and moving elements at an extremely low bitrate. Most normal film and video content doesn’t gain anything by adding manual keyframes. Figure 5. The video and audio settings used in the final project Encoding Settings Now that we’ve got the source all set up, let’s dig in to the precise encoding settings that we can set in Expression Encoder (Figure 5). Many of these concepts are applicable to other tools using the VC-1 Encoder SDK (details at www.microsoft.com/resources/mediaand entertainment/vc-1encodersdk.mspx), and many are applicable to other codecs as well. The original FLV file was 640x480 with VP6 video at 488Kbps (the encoder was set to 400Kbps, but VP6 is infamous for overshooting the requested bitrate in aggressive compression) and MP3 audio at 48Kbps. For an apples-to-apples comparison, we’ll stick with the original settings so the file will go at the same size. Additionally, we’ll target a peak bitrate of 1Mbps (the worst-case scenario of the maximum video and audio bitrates at the same time), which will stream without buffering to most consumer broadband connections today. VIDEO Figure 6. I set the Video Complexity to Best (5), since it’s a short clip at a reasonable frame size. • Frame Rate: Source—We want to capture all the motion in the source perfectly (29.97 fps in this case). • Keyframe Interval: 15 seconds—The longest gap between markers in the source is a hair less than 15 seconds, so this will prevent keyframe popping between cards, since our marker-based keyframes will “reset” the keyframe interval each time they are F inserted (Figure 6). • Profile: VC-1 Advanced Profile—VC-1 supports Simple, Main, and Advanced profiles. While Main is more compatible with older versions of Windows Media Player and generally provides equivalent quality, this is a Silverlight-only project, and we want to use Advanced so we can use Dquant, as discussed later. • Mode: VBR Peak Constrained—This is a progressive download project, so VBR Peak Constrained is the optimal encoding mode. It’ll reduce bitrate on the easy parts of the video and then spend those bits on the hard parts. • Bitrate (average): 488Kbps—This matches the original FLV’s actual bitrate. • Peak bitrate: 895Kbps—Combined video plus audio (we’ll use 96Kbps later) plus overhead (9Kbps in this case) max bitrate is a consumer-broadband-friendly 1,000Kbps (1Mbps) total. 28 STREAMING MEDIA August/September 2008 • Peak Buffer Size: 15 seconds—This way the buffer duration can contain an entire GOP (a keyframe and frames that reference it). Having the GOP length and the buffer size match helps make sure the keyframes can pull bits from the full range of surrounding frames. • Width and Height: 640x480—This is the same as the source. The original project had both 320x240 and 640x480 encodes, but they used the same data rate, so I’m doing just the 640x480. The Silverlight embed can be set to the desired size to give the same end result. AUDIO • Codec: WMA—We’re targeting Silverlight 1.0 compatibility, so we need to use the legacy WMA codec. It’s still better bit-for-bit than the original clip’s MP3. We could use WMA Pro if we were targeting Silverlight 2.0. • Mode: VBR—One nice thing about the WMA family of codecs is that they support the full range of rate-control modes of the Windows Media video codecs. Using VBR audio raises the bitrate on the hard parts and lowers it on the easier parts, making for more consistent quality and avoiding those times where the audio sounds great except for cymbals or some other percussion. http://www.microsoft.com/resources/mediaandentertainment/vc-1encodersdk.mspx http://www.microsoft.com/resources/mediaandentertainment/vc-1encodersdk.mspx

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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