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Tricks to sharpen your YouTube spots.

While you can spend hours on You Tube watching everything from Obama Girl to stupid cat tricks, many of our clients have also found a much more practical use for YouTube: distributing clips of television spots to their colleagues for approval.

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It wasn't long before these clients noticed the quality wasn't as good as what they saw in our edit suite. YouTube significantly reduces image quality in the interest of Internet bandwidth. You can't control much about the compression process at YouTube, but there are things you can do to enhance the quality of the finished product.

In a search for the very best process for our clients, I submitted hundreds of test clips (continued from page 680

to YouTube. But before I share some of my findings, let me go over a few of the basics of video compression.

One of the major misconceptions of video compression confuses the player technology with the codec. A codec (Coder-Decoder) is the algorithm used to squeeze out redundant or unnecessary data from video in order to shrink file sizes. It's a delicate balancing act between reducing data and leaving an acceptable image behind. This compromise is important to understand since whatever you submit to YouTube will be compressed again with a Flash Video codec. The original compression submitted to YouTube will suffer some degradation, but avoiding additional cascading compression artifacts is the key.

Video compression, present in all forms of digital video these days, will compromise the image quality at least slightly. Each codec leaves its own footprint on the video. Depending on your submission format, visible compression artifacts may multiply themselves tobecome more noticeable when uploaded to YouTube, so care must be taken to choose your upload format widely.

The player you see on a computer is just a way of displaying and controlling the video. Compressed video is typically packaged, transported and displayed through a "container." Software players, codecs and container technologies are really three separate pieces orchestrated by compression software. The actual compression is controlled by the codec, then the compression software wraps the compressed data into a container. The player understands how to unpack the container and extract the payload for display.

Blanket statements about which player technology is best for submission to YouTube become moot when considering all the other factors, especially the codec involved. Some player technologies will force you into a codec that is less than optimal for YouTube submission.

For example, Microsoft's Windows Media Player uses an underlying codec, the most common being the older Windows Media 9. Windows Media is really a container technology that favors its own codec and player. The Windows Media codec gave one of the worst performances in my YouTube tests.

RealMedia makes a player that primarily uses its own codec and container but will play other codecs and container technologies. RealMedia will play assets using the MPEG4 container and the H.264 codec. However, RealProducer only creates RealMedia files, which are not accepted by YouTube.

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Adobe's Flash technology (used by YouTube) is a container that understands a limited set of codecs but has a broad range of player will also understand MPEG3/H.264 encoded assets.

Apple's QuickTime is yet another container technology that understands hundreds of different codecs. QuickTime is arguably the crown jewel of multimedia because it is so flexdible. When creating QuickTime movies, you'll also need to define exactly which codec to use and what data rate to assign.

Today's most common QuickTime container is MPEG4. The most common codec is H.264, as found on iPods and iTunes. YouTube will accept a broad range of codecs encapsulated as QuickTime, as well as AVI and MPEG.

Having submitted hundreds of test clips to YouTube, I've drawn four main conclusions about how to address some quality issues.

Codec Selection

The original file uploaded to YouTube gets recompressed to Flash Video (.FLV), no matter what you've submitted. MPEG4/H.264 gave the cleanest results from YouTube. There are other MPEG4-compliant codecs available, such as Xvid and DivX, but they did rather poorly in our tests compared to H.264. The DV codec is also not a bad choice, but the files are relatively large to upload.

Scaling

Resizing existing video will destroy a picture. YouTube will resize whatever you upload to 320x240 and artificially scale it up again to 480x360 for display--a double-scaling whammy. A 640x480 original would be best to upload because it's an exact multiple of the resultant 320x240 YouTube video. If your submission is not an exact multiple of 320x240, as a professional video pixel count of 720x486 would be, expect some blurring. The entire image will be remapped to an odd number of pixels in a process called "interpolation," which is particularly damaging in the vertical dimension. To avoid this artifact, it may be better to crop vertically six lines from the 486-line original to create a 480-line-tall image. This will then scale perfectly to 240 vertical pixels.

Scaling, Take 2

Forget everything in the previous paragraph if you want to use YouTube's higher quality playback option. Within a half hour of your original FlashVideo file being made available for playback, YouTube also makes an MPEG4/H.264 version available. It has a native pixel size of 480x360. That size doesn't exist in nature and there's no graceful way of creating an artifact-free submission video from common video standards. That said, the higher pixel count is certainly welcome. To access the higher resolution YouTube playback, type "&fmt=18" behind any YouTube URL (without quotes). YouTube also makes a valiant effort to detect and correct wide-screen assets and force them into a 4:2 window using letter-boxing. Because of that, I've encountered some unexpected scaling results uploading odd pixel counts. Your mileage may vary.

Data Rate

Each codec has a working range for data rate; the trade-off is between file size per second of video and image quality. In theory, choosing the maximum data rate should get you the best image quality. With some codecs, this is overkill and will only extend the time you wait for the upload to happen. Choose a reasonable data rate that balances file size against quality.

Google purchased YouTube about a year ago and has rapidly made several significant technical changes. Unfortunately it doesn't appear possible to directly upload a finished compression to YouTube. The recompression phase must be tolerated, and the inherent scaling issues respected. Perhaps that will change in the future.

Steve Wiedemann is senior vice president and chief technology officer at Henninger Media Services in Arlington, Va.
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Title Annotation:Playbook
Author:Wiedemann, Steve
Publication:Campaigns & Elections
Geographic Code:1USA
Date:Aug 1, 2008
Words:1096
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