Streaming Media - December 2008/January 2009 - (Page 46)

Figure 4. In a nutshell, H.264 (center) was generally best, with VC-1 (left) getting blocky and VP6 (right) getting blurry. Figure 5. H.264 still looked better than half-resolution VC-1. can deliver stunning quality, one of the obvious lessons from the Summer Olympics, where Silverlight quality was better than what I saw on my TV. Still, just for fun, I produced another set of files from the After Effects intermediate file at 1,200Kbps, an increase of 50% over the vendor-submitted files. VC-1 still exhibited many of the same problems noted above while H.264 was nearly artifact-free, though still having problems with panning motions. From what I’ve seen and from what you can see yourself at www.doceo.com /HDcomps.html, if you do choose VC-1, you’ll have to encode at a higher data rate than you would with H.264. Addendum After I completed my initial analysis, Microsoft came back with one more encoding iteration that uses a little-known and even less-available encoding option: specifically, the ability to scale the video from 1280x720 resolution to 1280x544 (the single field height from 1080i) during compression, then scale it back to full resolution during decoding. While too late to redo the analysis presented previously, I wanted to have a look and see if the new technique would change the results. First, the encoding details: Microsoft did not implement this feature in Expression Encoder, and it was available in only one of the eight encoders in my office, though it didn’t work in my tests—all files were encoded to full resolution. To produce the file, Microsoft used an open source encoder called AVS2ASF that was developed by the Doom9 community and can be downloaded at http:// kurt 46 STREAMING MEDIA December 2008/January 2009 noise.free.fr/index.php?dir=misc. AVS2ASF is one of those intuitive command line tools that we nonprogrammers know and love, and the command line argument that Microsoft used to produce the file is available at www.compression matters.com, along with the file itself. Note that the fact that the file is subsampled during encoding is completely transparent to the viewer. That is, when the file plays, information in the file header instructs the playback program to decode and scale the video to its full resolution, and the person watching the video is none the wiser. With all this as a prologue, how was the quality? Overall, it was better than the full-resolution version with significantly fewer blocks and background artifacts, though low-motion shots were also noticeably blurrier. Most importantly, however, the subsampled version never exceeded the output quality of VP6 or H.264, as you can see for H.264 in Figure 5. This doesn’t mean that the technique doesn’t have merit, as it may be useful in scenarios where you want to retain big-screen video but minimize data rate. Still, the technique must be used with caution when producing for Silverlight because while Windows Media Player can scale using your graphics processor, Silverlight can only use the host CPU, which may slow playback on slower target computers. Jan Ozer (jozer@doceo.com) is a frequent contributor to industry magazines and websites on digital video-related topics and is the author and producer of the Critical Skills for Streaming Producers family of tutorials. Comments? Email us at letters@streamingmedia.com, or check the masthead for other ways to contact us. http://kurtnoise.free.fr/index.php?dir=misc http://www.compressionmatters.com http://www.compressionmatters.com http://www.doceo.com/HDcomps.html http://www.doceo.com/HDcomps.html http://kurtnoise.free.fr/index.php?dir=misc

Table of Contents Feed for the Digital Edition of Streaming Media - December 2008/January 2009

Streaming Media - December 2008/January 2009 Table of Contents User-Generated Politics Netflix Needs a Business Model Technology and Business Trends by the Numbers Improving Video Color Quality What Makes for Compelling Video? Game On: Bringing the NHL to IPTV Give! The New Era of Corporate Communications New Video Frontiers: Taking It Beyond the PC The HD Showdown: Codec Vendors Battle It Out for Supreme Quality The Ultimate Guide to Creating Online Video Content That Works, Part 2 Planning for Webcasting Success: Considerations for Deploying an Enterprise Video Communications Platform All Mobile Devices Are Not the Same Datmedia Datpresenter LSI Tarari Encoder Accelerator LCPX-6140 Gomez Active Streaming XF Transcoding for Global Reach Executive Visions 2009 The Revolution Is Being Televised

Streaming Media - December 2008/January 2009

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.