王备 – 音乐书简

如果你在家里看电影而不是去电影院，如果你追求卓越品质，那么，最好花点时间看看此文。

首先，看看这段测试视频。注意画面下半部分，是不是令人眩晕？小画面如此，想象一下，放大到40寸以上会怎样呢？

如果你看过之后觉得可以接受，那么请略过此文，以免浪费宝贵时间。

接下来开始讨论这个问题的成因以及解决方案。

【关于成因】

        电影胶片每秒钟播放24格图像（实际是48格），也就是所谓48HZ，而大多数电脑和电视则不能实现48HZ显示，一般为50HZ、60HZ、75HZ或85HZ，由于这些数值并不是48HZ的整倍数，中间转换就会是有损的，从而导致了上面视频例子中的运动画面抖动不均，术语叫做“Motion Blue”。

           更具体的信息推荐阅读这篇发表于“chip新电脑”杂志上的文章：
        24P格式：胶片质量的高清画面输出 （需要你安装有PDF阅读器）

        好在，目前这种状况正在有所改善，松下、索尼等大牌厂商已经推出了支持24P电影模式的平板电视，同时，支持24P格式输出的高清播放机也已经很容易买到。同时，PS3以及蓝光播放机也都支持24P输出。接下来的问题是，电脑用户怎么办？

        可悲的是，几乎所有家用电脑和显示器都无法实现24P格式的播放和输出，所谓的“高清硬件解码加速”技术，对于24P转换缺陷Motion Blue仍然于事无补。不过，此时也并非完全绝望，下面转帖一篇文章：

The State of 24p Playback on a Home Theater Computer

作者：Carlton Bale
原始链接（http://www.carltonbale.com/2008/11/the-state-of-24p-playback-on-a-home-theater-computer/）

To get the best video quality playback possible for movies in a home theater, it’s necessary for the refresh rate of the source component to match the refresh rate of the display. One of the most common problems stems from the fact that most movies are 24 frames per second while most televisions are 60 frames per second (approximately.)  It’s not a simple mathematical conversion to get 24 fps to scale to 60 fps. There are processing fixes (reverse telecine) to overcome this problem, but the frame rate of the source material must be properly detected and the proper correction applied. The best solution is to send the original untouched 24 fps signal from the player, through the receiver, and on to the display, where the frame rate can be doubled / tripled / quintupled without any skipping or judder.

The problem for users of Home Theater Personal Computers (HTPCs) is that there are very few hardware combinations that will properly pass the original 24 frame/second signal digitally to the receiver/display; the video drivers don’t support 24 Hz output properly.  One obvious example of this is the latest motherboards with the Intel G45 chipset. There is a setting in the HDMI video drivers for 24p, but the resulting video has noticeable jerks/pauses a couple of times a minute, apparently due to the driver improperly matching the output frame rate with the input frame rate.

Nvidia 9300 and 9400 chipsets – the first solution for HTPC 24p

The only exception of which I’m currently aware is motherboards based on the new nVidia 9300 and 9400 chipset. Multiple sources have confirmed that 24p playback is flawless over HDMI. Several vendors, including Asus (P5N7A-VM) and Gigabyte (GA-E7AUM-DS2H), have just released motherboards based on these chipsets.

(I plan on upgrading both of my HTPCs to the Gigabyte motherboard. Since Protected Audio Path is no where on the horizon, I see no need to wait.  Surprisingly, this is the cheapest upgrade I’ve done, because the motherboard contains everything I need for video, audio, and Blu-ray video decoding and I can use my existing CPUs, RAM, hard drives, cases, and power supplies.)

The downsides of 24p on a HTPC

The downside of setting the output of the HTPC to 24 Hz is that not everything is recorded at 24 Hz. Television shows are at 60 Hz. So if you’re watching a movie, you select 24 Hz and if you’re watchined recorded TV or TV on DVD, you select 60 Hz.  This is not automatic; you manually have to make these changes youself. So while a bottom-of-the-line Blu-ray player can automatically switch to the correct frame rate, an expensive and highly flexible HTPC cannot.

The simplest way to change the frame rate is to go to the video driver control panel and make the appropriate setting. But this is not very elegant for a HTPC. Instead, it possible to assign shortcut keystrokes to each resolution and map those to your remote control. This is a pain to setup, but it means that a press of the button switches between the two.
Theoretically, it’s possible for a program such as My Movies to store the appropriate framerate for each movie / show in its internal database and issue the appropriate "change video refreash rate" command when each is played, but I don’t think this is a supported feature yet.

What about 120 Hz?

A lot of flat panels advertise their 120 Hz refresh rate. This is the output video refresh rate of the panel itself, not the input refresh rate. The highest-possible refresh rate that is supported by HDMI is 1080p/60 Hz. No source component (HTPC or stand-alone DVD or Blu-ray player) can output 120 Hz over HDMI.

Conclusion

If you want a perfect video frame rate with no jerkiness or stutters over HDMI, it is possible on a HTPC using the latest Nvidia chipset. However, you manually have to change the output refresh rate of the video card, and knowing the correct framerate of the source materail is not intuitive. This is the price you pay for having a beautiful browesable for instant movie playback.

        简而言之，想让电脑实现24P信号输出，条件是使用nVidia刚刚发布的9300、9400芯片组主板，但是，显示器呢？什么样的显示器可以接收24P信号呢？最现实的办法是直接使用支持24P电影模式的平板电视。至于电脑显示器，目前，老式CRT显示器有一些是可以的，但谁还用啊？液晶显示器，现在知道的只有EIZO和HP两个品牌的高端专业产品可以支持24P格式，其他所有民用液晶显示器统统不可以。

        尽管所有LCD厂商都在嚷嚷着所谓支持全高清，但实际上，你买回家看电影的时候，就会是最上面视频举例中的那个样子。如果你试图通过某些工具强制将刷新率改为72HZ（24的整倍数）或96，下场会很惨。只能寄希望于厂商们尽快将24P电影模式加入到液晶显示器上来。不然，还是老老实实去买支持24P电影模式的平板电视吧。

        先写这些吧，如果将开头那段视频换成高清1080P，您对它的移动抖晃表示接收，请接受我小小的道歉for您的时间，同时也请接受我小小的BS…

【完】