user13877: For one movie, mkvinfo says:
|   + Pixel width: 704
|   + Pixel height: 480
|   + Display width: 853
|   + Display height: 480

What are these values exactly? Why the difference?

user1871: The pixel values refer to the actual number of samples stored per frame. The display values refer to the dimensions that the player should render the video at. The ratio of 853/704 = 1.212 is the pixel or sample aspect ratio. This is an example of  non-square pixels, a legacy of analogue video signals and usually seen in digitized forms of NTSC/PAL format signals. 

13877: <p>For one movie, <code>mkvinfo</code> says:</p>

<pre><code>|   + Pixel width: 704
|   + Pixel height: 480
|   + Display width: 853
|   + Display height: 480
</code></pre>

<p>What are these values exactly? Why the difference?</p>
 1871: <p>The pixel values refer to the actual number of samples stored per frame. The display values refer to the dimensions that the player should render the video at. The ratio of <code>853/704</code> = <code>1.212</code> is the pixel or sample aspect ratio. This is an example of  <a href="https://en.wikipedia.org/wiki/Pixel_aspect_ratio" rel="nofollow">non-square</a> pixels, a legacy of analogue video signals and usually seen in digitized forms of NTSC/PAL format signals. </p>
