如何MPEG4 COM pression工作？ [英] How does MPEG4 compression work?

问题描述

可以用简单明确的方式MPEG4工作如何COM preSS数据谁能解释。我最感兴趣的视频。我知道有不同的标准或部分给它。我只是在寻找predominant整体融为一体pression方法，如果有一个与MPEG4。

Can anyone explain in a simple clear way how MPEG4 works to compress data. I'm mostly interested in video. I know there are different standards or parts to it. I'm just looking for the predominant overall compression method, if there is one with MPEG4.

推荐答案

MPEG-4是一个巨大的标准，并采用多种技术，实现了高玉米pression率，这是可以胜任的。

MPEG-4 is a huge standard, and employs many techniques to achieve the high compression rates that it is capable of.

在一般情况下，视频融为一体pression涉及扔掉尽可能多的信息尽可能同时具有对最终用户的观看体验的影响最小。例如，使用二次抽样YUV代替RGB减少了一半的视频大小马上。这是可能的，人眼对颜色不太敏感比它要亮度。在YUV，Y值是亮度，及U和V值重新present颜色。因此，你可以扔掉一些的颜色信息，从而减少了文件大小，没有观众注意到任何区别。

In general, video compression is concerned with throwing away as much information as possible whilst having a minimal effect on the viewing experience for an end user. For example, using subsampled YUV instead of RGB cuts the video size in half straight away. This is possible as the human eye is less sensitive to colour than it is to brightness. In YUV, the Y value is brightness, and the U and V values represent colour. Therefore, you can throw away some of the colour information which reduces the file size, without the viewer noticing any difference.

在此之后，大多数COM pression技术利用2冗余特别的优势。第一个是时间冗余，第二个是空间冗余。

After that, most compression techniques take advantage of 2 redundancies in particular. The first is temporal redundancy and the second is spatial redundancy.

时空冗余注意到，在一个视频序列中的连续帧非常相似。通常，视频会以每秒20-30帧，并没有什么太大的变化的顺序在1/30秒。采取任何DVD和暂停它，然后将它放在一个帧，并注意2图像的相似程度。因此，而不是独立地编码每个帧，MPEG-4（和其它的COM pression标准）只连接$ C C连续帧之间的差异$（使用的motion估计以找到帧之间的差）

Temporal redundancy notes that successive frames in a video sequence are very similar. Typically a video would be in the order of 20-30 frames per second, and nothing much changes in 1/30 of a second. Take any DVD and pause it, then move it on one frame and note how similar the 2 images are. So, instead of encoding each frame independently, MPEG-4 (and other compression standards) only encode the difference between successive frames (using motion estimation to find the difference between frames)

空间冗余需要的，在一般横跨图像的颜​​色s- $ P $垫往往是相当低的频率的事实的优点。我的意思是相邻像素往往有相似的颜色。例如，在你的图像穿着红色的跳线，所有的重present你的跳线将有非常相似的颜色像素。它是可以使用的DCT变换的像素值变换到频空间，其中一些高频信息可以扔掉。然后，当反向DCT处理（解码期间），该图像是现在没有扔掉的高频信息。

Spatial redundancy takes advantage of the fact that in general the colour spread across images tends to be quite low frequency. By this I mean that neighbouring pixels tend to have similar colours. For example, in an image of you wearing a red jumper, all of the pixels that represent your jumper would have very similar colour. It is possible to use the DCT to transform the pixel values into the frequency space, where some high frequency information can be thrown away. Then, when the reverse DCT is performed (during decoding), the image is now without the thrown away high-frequency information.

要查看扔掉高频信息的影响，开放式MS画画一系列重叠的水平和垂直的黑线。将图像保存为JPEG（也使用DCT的COM pression）。现在放大上的图案，注意线的边缘是如何不尖锐了，并且有点模糊。这是因为某些高频信息（从黑到白的转换）期间已经融为一体pression扔掉。 阅读本与漂亮的照片

To view the effects of throwing away high frequency information, open MS paint and draw a series of overlapping horizontal and vertical black lines. Save the image as a JPEG (which also uses DCT for compression). Now zoom in on the pattern, notice how the edges of the lines are not as sharp anymore and are kinda blurry. This is because some high frequency information (the transition from black to white) has been thrown away during compression. Read this for an explanation with nice pictures

有关进一步阅读，这本书是相当不错的，如果有点沉重的数学。

For further reading, this book is quite good, if a little heavy on the maths.

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