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Testing YouTube's 720p HD Encoding

Editor's note: The complete version of this article appears on Jan Ozer's Streaming Learning Center website.

I just finished testing YouTube's new H.264-based HD video, and it is very compelling. You can see the video I uploaded at the YouTube site, click here.

Briefly, to have your video encoded in HD, all you have to do is upload the video in 720p format. Note that the usual file size (1GB) and duration limits (10 minutes) apply. You can upload in a variety of formats; I used H.264. YouTube first creates a very ugly 320x180 video for normal viewing, then the big enchilada.

Video Encoding Parameters
What do we know about the video? Well, thanks to the information screen of the free MediaInfo video analysis tool, we know quite a bit. For starters, we can see that YouTube is producing the file at 720p (1280x720) at a video data rate of about 2Mbps, which translates to a fairly economical .072 bits per pixel. By way of comparison, Apple used .089 bits per pixel for a recent marketing video, while Cranky Geeks uses .072, pretty much identical to YouTube.

On the H.264 front, YouTube is encoding with the High profile with CABAC enabled. These are the specs I've been recommending for awhile, but few real world publishers have actually used them, so it's nice to get affirmation from the largest video publisher in the world. Of course, those producing with Apple Compressor—including, presumably, Apple—can't use either advanced parameter because Compressor doesn't support CABAC or the High profile. In addition, only the most recent versions of the QuickTime Player could play back the High profile, so if you were producing for QuickTime playback, the Main profile made more sense.

On the other hand, the Flash Player can play all levels of the High profile, as well as Main and Baseline, so when producing H.264 for Flash, High is the way to go. Interestingly, though not shown, YouTube produced the file with an MP4 extension for playback in the Flash Player, not the F4V. Flash Player doesn't care, it will play either format, but F4V is the extension used by most recently released encoding tools.

Audio Encoding Parameters
On the audio front, YouTube encoded with AAC LC, with two channels (e.g. stereo) to a data rate of 93kbps. I would have used mono here to save a channel, but nobody asked. If you've been encoding with MP3, you probably think that the 93kbps is miserly, but AAC LC is much higher quality compression, so should approximate at least 128kbps MP3, if not higher.

Other Encoding Parameters
What else do we know about the file? Thanks to Inlet Semaphore, we can really dig into the file for details. Click here to see the Semaphore file analysis output and read further analysis.

Jan Ozer (jan at doceo.com) is a streaming media consultant and frequent contributor to industry magazines and websites on streaming related topics and the author of Critical Skills for Streaming Producers, a mixed media tutorial on DVD published by StreamingMedia.com.

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