Video Compression Workshop – Helpful Advice (part 3)

Wednesday, July 30, 2008 Filed in: Video | Education

Need to get your video delivered to your audience? Then there’s probably going to be some compression involved. Don’t let hardware or software get in your way. Let’s take a common sense approach to getting your video out there.

Pick Your Power

There are tons of compression tools out there, but the pro apps offer important features like batch processing, multiple architecture support, and customizable presets. The five most popular options are:

Apple Compressor (www.apple.com) Bundled free with Final Cut Pro or DVD Studio Pro. However it can’t output some Window’s oriented formats and it is occasionally cranky (requiring restarts, trashing preferences, and even re-installs to get back on track).

Canopus ProCoder (www.canopus.com) a versatile PC-only solution for encoding video in a variety of formats. It offers both a guided and an expert mode to setting up your jobs.

Autodesk Cleaner and Cleaner XL (www.discreet.com) The granddaddy of encoding utilities. It’s suffered from changing ownership several times and hasn’t seen much development lately.

Telestream Episode and Episode Pro (www.flip4mac.com) This product offers hooks into Apple Compressor and offers a variaety of additional formats that Mac users need.

Sorenson Squeeze (www.sorenson.com) An easy to use compression utility that also unlocks some specialty formats like Flash Video. Version 4.1 (a free upgrade) build in support for Windows Media files on the Mac Platform by using Flip4Mac (not a free upgrade - $99/$179).

Videosquish

Looking for a smaller download? The biggest changes you can make are window size and frame rate. These savings are before you’ve even gotten around to applying the compression algorithms. Pro’s will often compress the video to half size, but then flag the players to automatically show the video at 200% magnification. Large window, but tiny files.

SCREEN SIZE
Half Screen 75% reduction in file size
Quarter Screen 94% reduction in file size

Your video file is likely recorded at approximately 30 fps. This is needed for a television display, but not important for most Internet or CD-ROM video.

FRAME RATE – 30 fps material
15 fps 50% reduction in file size
10 fps 66% reduction in file size

These file savings can be combined, which can result in huge savings of download time or disk space.

Hip to be Square

There’s a good chance you are working with non-square pixels in your digital video clip. Computer pixels are square in shape, and you’ll need to compensate. Here are some of the most common sizes.

4X3 Aspect Ratio 16X9 Aspect Ratio
640 X 480 640 X 360
480 X 360 480 X 270
320 X 240 320 X 180
240 X 180 240 X 135
160 X120 160 X 90

Stereo, or No?

Most professional videos have two (or more) channels of audio. This can cause unnecessarily large file sizes and playback problems for viewers who listen on mono speakers. While you’re attracted to Stereo, give Mono some serious thought.

Stereo Dialog could result in many users not being able to hear the audio through their built-in speaker. Always pan dialog tracks to center before making your self-contained or reference clip to encode.
• Stereo data is twice the size of mono data. Get the size down.
• Unless you’ve got some dramatic environmental effects or music going on, Stereo is just overkill for the personal computer environment.
• If you really want stereo, look at your format of choice to see if it supports Joint Stereo. This will only save separate data for each speaker when there is a difference between the left and right channels. This can save a lot of space.

Flicker Fix

If you shot your video using a traditional standard def camera, you likely have interlaced video. On a Television this produces smoother motion, on a computer it produces junk. You’ve got two approaches to take

If the video is being acquired solely for web or theatrical you can shoot Progressive (such as 24P, 25P, or 30P). If your client likes the look, they may want to shoot 24P anyways.
2 Apply a de-interlace filter to your clip to all video shot with interlacing. If you are going to be producing several compressed formats, you may want to pre-process the source sequence by adding a de-interlace filter in your NLE. If you have the option, you may need to specify which field to use. For digital formats, both NTSC and PAL, you should choose lower field first.

Get the Wash-Out

One common client complaint is that the video often looks washed out on their computers. This is because video and computers operate in different color spaces (YUV vs. RGB). Video signals operate between an RGB value of 16 thru 235. Computers use an RGB value of 0 thru 255. You will need to restore the black and white point of your image. Look for an option called Black Restore and White Restore. To fine tune this effect, you will need to experiment with the amount and smoothness settings. Be sure to invoke your preview window to see the results before encoding with the settings.

The Wal-Mart Effect

Videophiles will tell you that consumer televisions ship with the reds boosted to ridiculous levels. Therefore a video file displayed on a computer will also need the saturation turned up a bit to meet your client’s expectations. This is to compensate for what I call the Wal-Mart effect. Consumer TVs have their reds over-cranked to make skin tones appear richer on their cheap tubes. Ignore your calibrated monitor and give it a 5-15% boost for that healthy skin glow. Consumers expect these rich skin tones, go with the flow and give them want they want.

Client-Ready

Looking to save some time? Be sure to check if your compression program has these power features. These are some great ways to get a little more done with less work.

Droplets – Save your compression setups as “mini-apps” on your desktop. Drag a source file onto the preset and it will load the proper settings for you.
• Normalize Audio – If your show is properly mixed, you can skip this option. However, many of our compression jobs use sources we didn’t edit. This safety option will bring your audio levels to a more consistent range.
• Fade In/Out – Instead of tying up an edit suite, you can do simple edits in your compression program. Mark your In and Out point, and let your compression tool perform an audio and video fade. Since many web pages use white backgrounds these days… confirm what color you should fade to.