Special Delivery: High-Def Video
Hulu makes all videos available in multiple resolutions, and it produces high-definition streams in H.264 format at 1280x720, with a total data rate of 2.5Mbps, including 11Kbps audio. Interestingly, Hulu will use the FLV container format for its H.264 video, not MOV. Hulu produces SD video using the VP6 codec and FLV format, with two configurations, 480Kbps (512x288) and 700Kbps (640x360), both including 64Kbps audio.
The clips are advertising supported, and generally start with a 5–10 second commercial—Cisco, Burger King, and Intel graced the clips I watched, with bugs and transparent advertisements popping up occasionally in shorter clips and short, fullscreen advertisements in others. Feng reports that Hulu chose the Flash platform because of its "very healthy" user base and customizability, and because there are identical players for Mac, Windows, and Linux platforms. Hulu chose H.264 for high-definition video because of its quality.
Hulu’s Flash Player is well-featured and lets the viewer rate the clip, provide problem-oriented feedback, create code for embedding the clip in a website, dim other regions in the browser, and play the video at full screen or in a separate window. The player also has progress bars that track both playback and clip downloading.
Hulu receives video from content suppliers in a number of formats, from pre-encoded FLV files to digital beta tapes. For its own encoding, Hulu uses multiple tools, processing most clips on its rendering farm via distributed encoding tools from Digital Rapids and Rhozet. Most videos encode to very high quality using Hulu’s standard parameters and procedures, but when Hulu needs to customize quality for particularly challenging clips, they typically use desktop encoding tool Sorenson Squeeze.
Hulu delivers all clips via progressive download, using Akamai as its CDN, even for clips launched from partner sites like AOL and Yahoo!. To date, most of the clips on the site are SD; the only HD clips I saw were 10 clips in the site’s HD gallery, but Feng reports that these are just the first step. For these clips, the Hulu blog reminds viewers that if their connections can’t keep up with the data rate, they can click Pause until the clip is fully downloaded, then resume playback.
Hulu also publishes extensive requirements for viewing HD on its site. This includes an internet connection of 2.4Mbps or higher, the latest Flash Player 9 build, and a 3GHz Pentium 4 for Windows with 128MB of RAM, and Intel Core Duo 1.83GHz with 256MB of RAM for the Macintosh, both with at least 64MB of VRAM.
Akamai is a leading CDN that delivered video for two of the three high-definition producers profiled here. I spoke with Suzanne Johnson, Akamai’s senior product marketing manager for digital media. During our discussion, it became clear that Akamai has given lots of thought to high-definition video, as evidenced by its HD video website, www.thehdweb.com, and a white paper available on the Akamai site entitled "Highly Distributed Computing is Key to Quality on the HD Web." Both are interesting and worth perusing.
Akamai launched TheHDWeb as a proof-of-concept portal to illustrate the high-definition video experience. Companies who provided content for the site include Apple, BBC Motion Gallery, CBS, Gannett, MTV Networks, and the NBA. Verizon is another content provider and touts its all-fiber ultra high-bandwidth FiOS network on the site.
In creating the site, Akamai adapted very traditional definitions of high-definition video, essentially 720p and 1080i. Supported formats include VC-1 and H.264/MPEG-4 AVC, submitted in MOV containers for QuickTime, as opposed to Flash playback. Suggested encoding parameters are 5Mbps for 720p files, with 1080i produced at 8Mbps.
When you visit the site, it tests your bandwidth. Assuming that you don’t have 7.5 Mbps downstream bandwidth, you’ll get a message allowing you to proceed but warning that you may experience difficulty. The site presents three files for each video, and data rate and other encoding parameters vary by provider. Akamai distributes all files via progressive download, and you can save the QuickTime and Windows Media files to disk for further analysis. I used a combination of Media Player, QuickTime Player, FLV Player, Inlet Semaphore 2.5, and Sliq Media’s WMSnoop to glean the following information from these files.