Preparing video for distribution on the Web or a CD-ROM can be downright depressing. You use top-notch gear to shoot your footage, digitize it onto a high-speed disk array, and edit and polish the final product until it glitters. But to put your video on the low-bandwidth realms of the Web or a CD-ROM, you have to compress it into a grainy, jerky clip that will make viewers wince. How does a quality-minded CD-ROM or Web video producer cope?
Having more control over the compression process is part of the answer, but you also need to master the black art therein. Currently no program provides more control over compression than Terran Interactive’s Media Cleaner Pro (MCP), whose broad array of features enables you to get the highest possible quality and the smallest possible file sizes. MCP also dovetails particularly well with Apple’s QuickTime 3 and the Sorenson Video compression technology that accompanies it (see “Harnessing a New Codec”).
On the following pages are a multitude of tips, tweaks, and techniques for mastering the finer aspects of compression with MCP 3 to achieve the ultimate balance of clean, lean, and beautiful video. Unless otherwise noted, everything here applies to both CD-ROM and Web video production.
Beyond the Wizard
If you’re a compression newbie, MCP’s Settings Wizard walks you through the process of specifying compression settings, asking you questions about a movie’s destination and content. But the wizard doesn’t give you access to MCP’s best quality controls; you access these via the Advanced Settings window (see “Where the Tweaks Live”). To display the Advanced Settings window, choose Advanced Settings from the Windows menu.
Media Cleaner Pro lets you save collections of compression settings so you can apply them instantly to other movies. A saved collection of settings is called, remarkably enough, a setting. MCP includes dozens of canned settings for common tasks, but chances are you’ll want to fine-tune them for your specific needs. When you do, use the Advanced Settings window’s Save As button to save your customized setting under a new name. This keeps the original setting intact as a starting point for future efforts.
If you have multiple machines running their own copies of Media Cleaner Pro, you can move customized settings between machines. Simply copy the appropriate settings files from the Media Cleaner Settings folder, found in the Media Cleaner Pro 3 folder. Better still, stash a Media Cleaner Settings folder on a file server, create an alias of it, and replace each machine’s Media Cleaner Settings folder with the alias. Now each machine’s copy of Media Cleaner Pro will access the settings folder on the server.
You’ve arrived at the perfect combination of settings for a given project and created a new settings file. To ensure that you don’t accidentally change the settings, use the Finder’s Get Info window to lock the settings file.
The Gamma Gap
Web designers are (or should be) intimately familiar with Windows’ gamma issue: Mac-created graphics often look too dark in Windows because PC monitors have a different gamma curve than Macs. The same applies to video clips.
Media Cleaner Pro makes gamma adjustments a cinch. With the desired setting selected in the Advanced Settings window, click on the Adjust tab and check the Gamma box. Move the slider to the right to brighten the movie.
Start at Thirtysomething
What’s the best gamma adjustment for optimum Windows playback? That depends on your movie, but a good starting point is 30. In general, if the movie looks a bit too light on your Mac’s monitor, it will look good on a PC.
Consider Platform-Specific Movies
If you’re creating movies destined for playback in QuickTime 3, consider creating two separate gamma-corrected movies, one for the Mac OS and one for Windows. Page 114 of the Media Cleaner Pro manual contains a cool tip for using QuickTime 3 reference movies to deliver separate movies transparently to Mac OS and Windows users.
Harnessing a New Codec
The Sorenson compressor/decompressor from Sorenson Vision (
) that accompanies QuickTime 3 provides smooth, sharp playback at much lower data rates than the venerable Cinepak codec does. But Sorenson brings new issues to the table, and applying Cinepak techniques to Sorenson often yields disappointing results. Getting the best results from Sorenson means, well, thinking different.
Where’s It Going?
For a Web-destined movie, first decide whether it’s important for it to stream in real timethat is, to begin playback almost immediately and to play without pause as the file downloads. For short moviessay, 30-second clips–c;nsider forgoing immediate gratification in the interest of better compression quality.
A movie compressed with a data rate of about 10K to 20K per second and a frame size of 240 by 180 pixels might take about a minute to load before playback begins. But the larger frame size and higher image quality may make that wait worthwhile. And if you put text on the page containing the movie, viewers will have something to distract them while the movie loads.
For movies destined for CD-ROMs, try a data rate of about 100K per second, with a 320-by-240 frame size and a 15-fps frame rate.
Keep the Red Out
A strange quirk of Sorenson’s underlying compression scheme is that brightly saturated reds compress poorly. Titles consisting of red text against a black background are likely to look particularly bad. Consider avoiding bright reds in clips that you’ll be compressing with Sorenson.
The Key to Keyframes
With Cinepak, it’s common to specify one keyframe every second. (A keyframe contains the complete video image; between it and the next keyframe are delta frames containing only those pixels that change.) Sorenson doesn’t need as many, and gives better results if you specify one keyframe every ten seconds or so.
The Sorenson codec that accompanies QuickTime is just a subset of the compression marvels that Sorenson Vision has created. The $499 Sorenson Developer Edition provides several additional compression features, some of which are accessible only through Media Cleaner Pro (see Reviews, November 1998).
The most noteworthy of the goodies in Developer Edition is variable bit-rate (VBR) encoding, which adjusts data rates on the fly to deliver the best quality for the scene at hand. VBR works particularly well with material that alternates between periods of low and high activity–f;r example, a title dissolving into a fast-motion scene.
One caveat you should be aware of is that VBR can increase compression time by a factor of three, so build a little extra time into your postproduction schedule if you plan to use it.
Bonus Refinement Tactics
There are additional ways to improve compression and minimize its artifacts. Assess the results of each tweak in Media Cleaner Pro’s Dynamic Preview window (see “Now Previewing”).
Turn Down the Noise
Video noise–e;pecially apparent in dimly lit scenes–c;mpresses poorly. In the Advanced Settings dialog box, check the Image tab’s Adaptive Noise Reduce box to apply a noise-reduction filter. The default option, Flat Field, is usually best.
You compression old-timers may be tempted to check the Blur box, since applying a slight blur to a clip was a common technique to improve Cinepak compression. But resist the urge to blur–ada;tive noise reduction provides the same benefits but does a better job of preserving edge sharpness.
Tweak the Contrast
Boosting a clip’s contrast slightly can improve compression by making almost-black areas completely black. Check the Adjust tab’s Contrast box, and drag its slider to the right 10 to 15 units.
Mask Your Talking Heads
For talking-head movies, consider using the Image tab’s Static Mask feature (see “Masking and Watermarking”). By masking out areas that don’t change from one frame to the next, you eliminate hard-to-compress video noise, enabling your codec to concentrate on compressing the movie’s main subject.
Crop the Garbage
When you capture video from an analog videotape, the resulting movie is likely to have several rows of dancing pixels at the bottom. This garbage gives your movie an amateurish look, and those dancing pixels are hard to compress. Use Media Cleaner Pro’s crop feature to remove extraneous junk; you can enter numeric values in the Advanced Settings window’s Image tab, or open the movie’s Source window and draw a crop rectangle.
Get Inflatable Assistance
So few software developers use the Mac OS’s balloon-help feature that you probably have never bothered to try it. Well, surprise: Terran Interactive has filled Media Cleaner Pro’s balloons with tips and succinct instructions. Check them out.
One of the best bits of advice, naturally, is to aim high at the outset. Media Cleaner Pro is a power tool, not a miracle worker. It can’t compensate for a bargain-basement camcorder, poor lighting, and an overcaffeinated camera operator. So keep in mind the standard rules of Web and CD-ROM video: use quality gear, light well, minimize panning and zooming, and use a tripod.
A contributor to Macworld since 1984, JIM HEID (
) writes and lectures about Web, video, and multimedia development.
Masking and Watermarking
Simplify your codec’s chore: eliminate hard-to-compress noise by creating a mask and using Media Cleaner Pro’s Static Mask feature. You can also create a watermark–f;r example, add your company logo to a movie’s lower-right cornerusing a similar technique.
1. From within a video-editing program, Apple’s MoviePlayer utility, or Media Cleaner Pro, export a representative frame of your movie as a PICT file.
2. Open the PICT file in Adobe Photoshop and create a new layer. In this layer, use the paintbrush tool to paint out areas in the background layer that don’t change between frames.
3. Hide the background layer by clicking its eye icon in the Layers palette, and use the Save A Copy command to save this mask as a PICT file. In Media Cleaner Pro’s Advanced Settings window, click on the Image tab, check the Static Mask box, and use the Set button to specify the PICT mask you just created.
Media Cleaner Pro 3.0’s Dynamic Preview window lets you evaluate the effects of your compression and optimization settings before you actually compress the movie. Its split-screen approach provides a before-and-after view of your settings.
To display the window, choose Dynamic Preview from the Windows menu (or press command-D). The window shows the same frame that’s displayed in the Source window; to display a different frame, activate the Source window by clicking on it and drag the QuickTime controller bar to the desired frame.
Drag the slider (A) to the left or right to change where the screen splits. Media Cleaner Pro also displays the approximate size of the currently displayed frame (B) so you can assess the shrinking skills of your chosen codec.
To preview the results of your optimization settings, check the right-hand Process box in the collection of four check boxes (C).
To preview noise reduction, check both Process and Compress on the right. Now both sides of the preview show the clip in its compressed form, but only the right side shows optimization and image-tweaking results. This lets you see how your settings will affect the quality of the final output.
To preview everything, check the Compress box on the left and both the Process and Compress boxes on the right. Now the left side of the preview window shows the original clip, and the right side shows how the final output will look. This preview mode is the slowest but gives the most accurate glimpse of your final product.
TIP If you see that your chosen codec is altering the image’s color balance, go into the Advanced Settings window and tweak the Hue and Saturation sliders under the Adjust tab until the color balance of both sides is the same. Then click on Update (D) or press command-D to update the preview.