2012年1月18日
By 1月时特约编辑
专题文章

Digital-Blonde Promises Better 编码; We Say 'Prove it!'

I got my start with compression technologies back in 1992 with a company called Iterated Systems, which licensed still image and video codecs based upon fractal compression. 当时, 我负责市场营销, 还写过一些夸张的新闻稿, 宣传册, 以及其他营销材料. In 1993, 我创办了Doceo Publishing, and my first product was a CD-ROM that benchmarked the video compression technologies of the day. This was pre-internet, of course; in fact it was pre-DVD.

在我从Iterated System过渡到Doceo的过程中, I went from writing compression-related marketing materials to disproving them, 多年来，我揭穿了自己的秘密. So when I get an email that includes a claim like the one below, it definitely perks my interest.

Better编码 is built on a proprietary transcoding system that knows how to interpolate the video/audio files using complex algorithms that result in much better file compression leaving the quality intact. On average our output files are 40 percent smaller comparing to any other solution at the same/better video quality.

This was from a company called Digital-Blonde, Inc, which runs a website called Better编码.com. 我基本上回应了, “证明它," which kicked off the process that resulted in this article, 我将探讨:

How Digital-Blonde's encoding algorithm compares to MainConcept and x264 output produced by Sorenson Squeeze 8.
作为这个的副产品，主概念H.264编解码器与x264比较.
如何H.在超低数据速率下，264输出与VP6相比.

测试程序

我的标准混合源SD测试文件是640x480x29.97 file that I typically encode at 500 kbps, of which 468 kbps is video, and 32 kbps audio. This is an aggressive configuration that results in a bits/pixel value of around .054; by comparison, CNN publishes its news videos at around .1 bits/pixel, while ESPN produces their higher-motion sports clips at .15岁及以上.

来支持他们的主张, Digital-Blonde制作了一个280kbps的测试文件, 或者468 KBPS降低40%, 这就产生了显微镜的位/像素值 .028. 就在这个过程开始的时候, 我收到了一个发货版本的Sorenson Squeeze 8, 其中包括x264和MainConcept编解码器, 所以我想我可以一举两得. 具体地说, I would see how x264 compared to MainConcept in Squeeze 8 and see how both compared to the Digital-Blonde file.

在挤8中工作

除了在Squeeze 8中添加x264编解码器之外, Sorenson also greatly expanded the encoding parameters available for both the x264 and MainConcept codecs. 例如, I counted over 65 configurable parameters for the x264 codec, MainConcept编解码器为33. 幸运的是, Sorenson包括每个编解码器的预设, 所以你不需要手动调整参数.

图1. x264预设在索伦森挤压8.

用于x264编解码器, 我使用了慢速预设(图1), which in my tests delivered about the same quality as the placebo preset in less the 25 percent of the encoding time. The MainConcept presets are presented as a number from 1 to 16; I used 16 since it only adds about 70 percent to encoding time compared to the default value of 10.

468 vs. 280kbps -毫无疑问

I first tested Digital-Blonde's assertion that it could deliver the same or better video quality at a 40 percent lower data rate. 如图2所示, 但这并没有发生, as the Squeeze clip retained noticeably more detail in many scenes. That said, I was impressed at the quality that Digital-Blonde produced at that low data rate.

更好的编码2

图2. 468 kbps的“挤压”优于280 kbps的“数字金发”.

That prompted me to level the playing field and produce all clips at 280 kbps, which provided the perfect testbed to compare the MainConcept codec with the x264 codec.

苹果与. 苹果(280 kbps对比)

当我比较编解码器或编码工具, 我制作比较文件, then make sure there are no dropped frames and that data rates are within 5 percent of the target. Then I consider two quality-related variables; still image quality and the presence or lack of artifacts during real time playback.

在280kbps的情况下，我得出了两个结论. 第一个, that the x264 output produced by Squeeze was of higher quality than the MainConcept output, 如图3所示, which includes all three test samples and the frame from the original video. Note how the detail in the MainConcept clip on the bottom right is almost completely obscured.

更好的编码3

图3. Both Digital-Blonde and x264 produced better quality than the MainConcept codec.

My second conclusion was that Digital-Blonde produced slightly better quality than Squeeze's x264 output, 但只有一点点, 这是使用一个简单的编码预设, 没有定制. Squeeze 8's interface lets you customize every x264-related option, 我花了一些时间来优化, 它本可以扭转局势. In addition, during real time playback, it's unlikely that any viewer would notice the difference. So, while Digital-Blonde's original claim of similar or better quality at a 40 percent lower data rate didn't hold true, 它确实是三个测试样品中质量最好的.

VP6怎么样??

总的来说，我对H.264保持在280kbps. Since many Flash producers still encode using VP6, I wanted to see how VP6 quality compared to H.264. 所以我用Squeeze 8制作了一个280 kbps的视频文件. 长话短说, 而VP6则在低动作序列中保持了自己的风格, even a little motion stirred up a swarm of very noticeable blocks.

更好的编码4

图4. 左边的VP6, H.右边264号.

他们把我们留在哪里了? Yet again, we learn that if something sounds too good to be true, it probably is. Digital-Blonde can take some solace in winning the overall quality title, 然而, 即使只差一个鼻子. 当使用相同的编码平台时，我们也看到了这一点, x264产生了比主要概念编解码器更好的质量. 注意，这与 2011 发现 of Moscow University's Graphics and Media Lab, which produces an annual quality comparison of H.264编解码器. 如果你想要最好的H.264质量，找到一个输出x264的编码器.

最后，如果你拒绝从VP6切换到H.也许是时候重新考虑那个决定了. H.264是永久免费的免费互联网播放, and Flash players can use the GPU on your graphics card to accelerate playback of H.264，但不是VP6. 所以H.对于大多数网络制作者来说，264的成本应该是一样的, 同时提供更高的质量和更高效的播放.