VD制作DivX4

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这是一个旧文档，文档的内容可能已经失去时效性，信息仅供参考。

需要说明的是：DivX4与DivX 3.x没有任何关系，只是设计者将DivX4编写成可兼容DivX3.x解码的平台。DivX4的各种性能都在测试中，使用时需注意这一点。　 安装好DivX4 Codec后，就可以进入VirtualDUB - [Video] - [Compression] 中选择到DivX4的编码器。 <div align="center"><SImg>501|large</SImg> </div> 选中“DivX Codec 4”后，点击[Configure]进入编码设定。 <div align="center"><SImg>502|large</SImg> </div> “General parameters”部分：首先有3种编码模式可以选择： 1-pass : 虽然本质上仍然是VBR，但相对比较接近CBR（固定码流编码），输出文件大小容易控制，但也意味着在一些大动态画面下难以有较好表现，和码流利用率相对不高。 1-pass quality based: 基本上等于是CBR（固定码流编码）模式的编码 2-pass, first/second pass(推荐): DivX4 支持2重VBR编码，这一点类同于SBC。此处设定为“2-pass, first pass”时，编码会建立一个LOG文件(LOG文件位置和文件名可以在“Two-pass encoding parameters”设定)，和一个很小的、并不能播放的AVI文件。建立了LOG文件后，可以在此处选择“2-pass, second pass”并进行第二重编码生成最终的AVI文件。 Performance/Quality: 推荐选择“Slowest”。“Slowest”质量最高，如果选择“Fastest”等于关闭运动检测，质量最差。 Output video bitstream: 此处设定输出文件的码流，可以根据实际需要设定。 Maximum keyframe interval: 此处设定限制最大的关键帧间距，默认值即可。DivX4也是一个基于VKI（动态关键帧）的编码平台。 Max CPU usage: 可以限定编码时的CPU占用率。 Deinterlace: 消除隔行拉丝的现象，但推荐不选用。因为在VirtualDUB的[Video] - [Filter]中的各种Deinterlace滤镜显然功能要完善的多。 “decoding parameters”部分： Default postprocessing level: 此处可以设定播放DivX时的解码质量。实际上是一种DivX4播放滤镜，可以去除画面种的色斑、马赛克等。设定为0即不使用。推荐设定为2-4，实际播放时可以根据自己的机器速度选择。 “encoding parameters”和“quality based encoding parameters”部分的设定主要作用于“1-pass encoding”，在“2-pass”两重压缩中并不起什么作用。 “encoding parameters”部分： Quantizers: 此设定为对输出文件大小的影响很大，特别是对于“1-pass encodeing”。此设定实际与NanDUB中的DRF设置的意义相同 Minimum quantizer: 设定画面的最小压缩级别。数值越低，输出画面质量越高。 Maximum quantizer: 设定画面的最大压缩级别。数值越高，输出画面质量越低。 Rate control averaging period: 此设定控制DivX4编码时同时监控计算的帧数。默认2000似乎不错，但更高的设定可以带来更好的质量，不过输出文件的大小会比较难控制。 Rate control reaction period: 此设定决定重算场景的速度。数值越大重算的速度越快、质量也越差，特别是在静态画面中。默认的10似乎不错。（注：有需要时，提高RCR也可以smoothed quality curve） Rate control up/down reaction: 即运动场景检测的敏感度。数值越低就越敏感，使用高码流的帧也会越多，文件也会越大，同时编码速度也会越慢。默认值20似乎工作得不错。This parameter kicks in when high motion scenes force the bitrate control module to lower the quality of the picture (equals increasing the quantizer) and it slows down further quality decrease. If you use very high values here you might end up in a situation where the codec doesn"t go above/below the median of the two values anymore. “quality based encoding parameters”部分： 使用1-pass模式压缩时，提高此处设定到85%以上时会使输出文件变大，请注意使用。 “Two-pass encoding parameters”部分：点击[select...]可以设定LOG文件的输出位置和文件名。 使用2-pass模式压缩时，有一个“Frame dropping”选项，可以设定丢掉一些编码器认为不需要的帧。不要使用此设定，会有同步问题，也不能流畅的回放。 注：that it"s possible to use the same first pass log file for several encoding sessions, but if you change the bitrate you will slowly use size predictability (depending on how much the bitrates used in first and second pass differ). In any case you should use the same performance/quality settings. Generally the files you will get from 2 pass encoding will match the values your bitrate calculator will give you. 选择“2-pass, first pass”模式，并设定完毕，点击[OK]，回到VirtualDUb主界面。点击[File] - [Save as AVI...]，设定一个文件名。选中“Add operation to job list and defer processing”，再点击[OK]。 <div align="center"><SImg>503|large</SImg> </div> 选中“Add operation to job list and defer processing”，并不会立刻进行压缩运算，而只是将任务添加到任务列表。直接回到[Video] - [Compression] - [DivX 4 Codec] - [Configure]，选择“2-pass, second pass”模式，其他设定不变。点击[OK]，再次回到VirtualDUb主界面。点击[File] - [Save as AVI...]，设定一个文件名。选中“Add operation to job list and defer processing”，再点击[OK]。点击[File] - [Job list]，进入任务列表： <div align="center"><SImg>504|large</SImg> </div> 这时点击[Start]，VirtualDUB会自动进行两重编码运算并输出DivX4视频AVI。 technical info about the 2 pass mechanism: During the first pass the movie is encoded in regular 1-pass mode and the following information is written to the logfile: if a frame was keyframe or delta frame, what quantizer was used, how many bits were used on texture coding, how many on motion vectors and how many bytes per frame in total. And here"s a sample line: Frame 103516: intra 0, quant 2, texture 10348, motion 1960, total 16245 Upon starting the 2nd pass the codec tries to open analyse.log. It will write:Total frames: 243767 Non-zero decisions: 243767 Avg quantizer: 6.971653 The first number is the total number of frames of the clip, the 2nd value the number of non dropped frames (should always be the same unless you use the frame dropping parameter which you really shouldn"t) and the average quantizer that will be used to encode the movie in the 2nd pass. Then it will write something like this for each frame: Frame 103516: PRESENT, complexity 25869, quant multiplier 0.500000, texture 2376, total 5471 Progress: expected 4265299248, achieved 4138620302, dq 0.913520, new quant 5 The first number is the framenumber, the 2nd indicates if a frame has been encoded (PRESENT) or dropped (SKIPPED), then the 3rd value represents the change from one frame to another (if you have two almost similar frames this value will be close to 0, if you have a lot of action the value will be high). The 4th parameter depends on the complexity (lower complexity = lower multiplier), then you get the number of bits used for texture and for the whole frame. The 2nd line refers to the frame that is to be encoded next. Expected and achieved show how well the codec bitrate prediction worked so far, ideally they should be close to each other (if they match you have perfect size predictability). dq is another quantizer multiplier used for rate control (in the example we are below 1.0 so we have to decrease the quantizer a bit). And the last field is the quantizer that is to be used for the next frame.

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