Compressão de vídeo

qual o melhor Codec vídeo que devemos usar?
um teste em extremetech: Video Codec Shootout.

para os mais apressados a conclusão neste artigo foi…

Final Thouhts (Video Codec Shootout)

Though we have certainly examined these four video codecs extensively, this article can by no means be considered the be-all, end-all on their relative merits. There are dozens of parameters and options when it comes to encoding video and, as thorough as we have been, there is much left unexplored. Variable bitrate and dual-pass encoding, for example, are common and useful features we didn’t cover here – unfortunately, they’re not entirely available in QuickTime 6.5 Pro for Sorenson3 or MPEG-4 encoding. That said, home video encoding is a slow and laborious process already, without waiting around twice as long for two-pass or variable bitrate encoding.

When it comes to visual quality, it’s difficult to say whether DivX 5.1.1 or Windows Media Video 9 looks better. It’s not hard to find specific instances in our test material where one outshines the other. It’s safe to make the generalization that the DivX encoded clips tended to have a touch more detail, but also a few more compression artifacts, than the WMV9 video. On the whole, watching the clips in motion and scrutinizing details over and over, it’s hard to recommend one over the other. DivX certainly encodes a whole lot faster, which can be a real concern when compressing large video clips. WMV9, on the other hand, has found its way into several consumer electronics devices, with a great many more on the way. The DivX codec is also available in a few devices, with more on the way, but support for WMV9 in upcoming DVD players, portable video players, and home media gateways is certainly stronger.

QuickTime 6.5 faired reasonably well when using the common Sorenson3 codec, only really breaking down in certain high-motion scenes. It’s also the fastest-compressing codec of the four tested here. The same cannot be said of Apple’s MPEG-4 implementation, however, which is absolutely awful. It shows plenty of artifacts even in relatively easy, low-motion scenes, and turns into a mess of blocks when the action gets even the least bit intense. These blocky artifacts are sometimes exaggerated in still shots, but in the case of our MPEG-4 clips, it looked just as bad in motion. This is not to say that all MPEG-4 will look this bad, but there are precious few free or cheap (sub-$50) programs that offer it at this time.

Obviously, nobody wants to wait hours to encode video, but that’s exactly what you’ll have to tolerate on a modern home PC. Dropping the resolution of your encoded clip naturally speeds things up a lot, but you’re still not going to do much better than real-time speed, so expect those home movie projects to bog down your computer for an hour or two if you don’t opt to trade off quality for performance. If you have a fair amount of video to encode, we recommend using a program that will let you queue up several clips and batch-encode them while you sleep. When it comes to speed, both of the QuickTime 6.5 codecs performed great, although we wouldn’t recommend either of them due to their less-than-ideal quality and lack of adoption in consumer electronics devices. If you’re looking to make video that will play on future DVD players, portable video players, and home media gateways, WMV9 is probably your best bet. A great many CE products shipping this year and next will support it. DivX has a reasonable amount of CE adoption as well, and may be the better choice for playback on a PC, as encoding times are much shorter and the quality is comparable.