使用mencoder时改变输入文件的分辨率

mencoder真是个很不错的工具。
如果想改变输出文件的分辨率可以使用 -vf scale 参数。
下面是从 man mencoder中抄的。具体的没有深入研究，简单的讲：
如果要保持宽高比，并且输出的文件的宽度为600，则这么写
-vf scale=600:-3

scale[=w:h[:ilaced[:chr_drop[:par[:par2[:presize[:noup[:arnd]]]]]]]]
              Scales  the image with the software scaler (slow) and performs a
              YUV<->RGB colorspace conversion (also see -sws).

                 <w>,<h>
                      scaled width/height (default: original width/height)
                      NOTE: If -zoom is used, and underlying filters  (includ‐
                      ing  libvo)  are  incapable  of  scaling, it defaults to
                      d_width/d_height!
                          0:   scaled d_width/d_height
                         -1:   original width/height
                         -2:   Calculate w/h using the other dimension and the
                         prescaled aspect ratio.
                         -3:   Calculate w/h using the other dimension and the
                         original aspect ratio.
                         -(n+8): Like -n above, but rounding the dimension  to
                         the closest multiple of 16.
有空可以深入研究一下mencoer