Choosing a Video Codec

To be completely descriptive, the reports don’t attempt to detail how to produce the files in each encoder. Rather, they point out hard-to-identify issues that can unnecessarily degrade video quality in some of the key encoding tools you’ll likely use to produce your video files.

Man Bites Dog
Choosing the right encoding parameters can be as important as deinterlacing and noise reduction for producing top-quality output. We compared the quality of Windows Media, Apple’s H.264, and RealVideo files produced using CBR and VBR techniques. Though VBR showed advantages in some of the categories, CBR was better in others.

With Apple’s H.264, we noticed that VBR visibly degraded low-motion talking head shots—as shown in Figure 5—which is probably not the tradeoff you want to make for slightly improved quality in dynamic scenes where the artifacts are harder to spot. Note that Apple created both of these files, not me, so save me the emails.

Figure 5

In our Flash trials, which pitted video encoded using the CBR Flash 8 Video Encoder against two VBR VP6 Encoders, Flash 8 bested both in several low-motion sequences. Clearly, strict adherence to the "VBR is better" mantra will cost you serious quality in some configurations.

Where Can You Play That Thang?
Work with me on this one. All Flash codecs play in . . . that’s right, Macromedia Flash 8. All Windows Media codecs play in . . . that’s right, the Windows Media Player. RealVideo plays in the . . . the Real Player. So obviously, all H.264 codecs play in the H.264-compatible QuickTime Player, right?

Well, no. Apple has implemented the Main Profile of H.264 into its encoders and players, as has Sorenson. However, encoded files produced with more advanced techniques, like the Advanced Simple Profile used in the Ateme Encoder featured in Nero’s line of products, won’t play in the QuickTime Player.

So, while the files look great, your viewers will have to download or otherwise acquire a separate player to play the video. This is definitely a workable solution if your audience is relatively small, but it’s still an important factor to include you your analysis.

You Look Marvy Against Black
Both of the images shown in Figure 6 were encoded with Microsoft Windows Media to our 100Kbps parameters. Quick, how much younger am I in the picture on the right? Er, scratch that. Instead, tell me why the image on the left looks so much better. Obviously, the primary difference is the background, which is stable, unmoving black velvet on the left, and a moving mass of people at a trade show on the right. Well, that and six years, but definitely going the wrong way.

Figure 6

Anyway, simply stated, the easiest way to make your streaming video look good, for most codecs, is to shoot against a flat black non-reflecting screen that sucks in the light, shows no detail, and allows the codec to focus solely on the money shot. Unfortunately, this rule isn’t universal; a couple of codecs faded very badly against black, and one started creating reddish artifacts.

Interestingly, in our 42 shots, we found several other background colors and schemes that produced more artifacts than King Tut’s tomb, as shown in the shot of lovely Larissa in Figure 7, adjusted with a tone map tool to highlight the banding most obvious on the left.

Figure 7

This is an artsy, two-camera shot with overlay, the back camera shooting the wide-angle view, with the side camera shooting a close-up of the mallets. Some codecs proved impervious to these issues; others produced artifacts on cue. For those, avoid these types of shots and backgrounds, and you can eliminate or minimize these problems before they get to the encoder. Overall, beyond your choice of codec and encoder, the easiest way to improve the quality of your video is to manage the background and motion content.

It’s All About Deinterlacing
Most encoding tools offer "noise reduction" or similar filters that are designed to improve the compressed quality of your video files. We tested these with most major encoding tools and found that they range from generally neutral to slightly positive, but occasionally negative.

Other than color correction and black and white contrast adjustments, which helped with most (but not all) codecs, we discovered that the most reliable way to improve video quality was to scale and deinterlace your video footage with a high-quality tool. Even this tended to produce subtle adjustments most noticeable on images with lots of motion and detailed hard edges.

For example, Figure 8 shows a clip from our test file that shows the champion golfer finishing his swing on a short par 3. On the left, the image was deinterlaced in AlgoSuite, an Adobe After Effects plug-in from Algolith (www.algolith.com), on the right using Adobe After Effects’ native tool, which is easily better than 99% of deinterlacing tools in streaming media encoders. Which starting point do you think would produce a higher-quality compressed file?

Figure 8

Of course, as Heinlein taught us, there ain’t no such thing as a free lunch, and AlgoSuite has some sharp edges, like glacial processing time and a somewhat confusing interface. Still, if you have the time and money (about $1,200), and a client to impress, it’s a great widget in your toolkit.

Always Leave ‘em Wanting More . . .
So that’s it; I could talk forever, but I’ve probably already given away too much. But what have we learned so far?

It’s not just a Real/Windows Media world anymore; Flash and MPEG-4 have achieved something very close to parity on many types of videos. When choosing an encoder to produce your video, remember that not all encoders produce equal quality, and that all encoding tools have their peccadilloes.

Beyond your choice of codec and encoding tool, creating the optimal background for your codec is the easiest way to improve video quality, but what works for one codec doesn’t work for them all. Finally, most of the noise removal filters out there are fool’s gold; a rare exception is a high-quality scaling or deinterlacing tool.