使用方法：extract file time step folder

time 設置時間長度

step 設置周期

均以秒（s）為單位

貢獻：1. 從視頻文件中周期性提取圖片；2. Windows下批處理程序的一些技術。

依賴：mplayer

todo: 目前周期最小為1s，可以擴展使頻率大於1Hz.

更詳細的內容可以參考：

http://blog.csdn.net/xuyaqun/article/details/6077917

http://blog.csdn.net/aa846555831/article/details/53400974

http://blog.csdn.net/yjfkpyu/article/details/3694990

 1 @echo off
 2 
 3 :: extract frames
 4 rem echo filename: %1
 5 rem echo time: %2 s
 6 rem echo step: %3 s
 7 rem echo folder: %4 
 8 
 9 if "%4" equ "" (
10   echo Usage: extract file time step folder
11   echo   file: mplayer can play
12   echo   time unit: s
13   echo   step unit: s
 
14   echo   folder: snap saved folder 
15   goto :end
16 )
17 
18 if not exist %4 mkdir %4
19 
20 set /A length = %2 / %3
21 echo length: %length%
22 
23 setlocal enabledelayedexpansion  
24 
25 set n=0
26 for /L %%i in (0, %3, %2) do (
27   :: progress info
28   set /A n += 1
29   set /A n = !n! %% 10
30
 
   if !n! equ 0 (
31     set /A nth = %%i * 100 / %2 
32     echo !nth! %%
33   )
34 
35   :: key command
36   mplayer -ss %%i -noframedrop -nosound -vo png -frames 1 %1 > nul
37 
38   :: save files because mplayer extracts frame in same name
39   set /A name = %%i / %3
40   move 00000001.png %4\!name!.png  > nul
41 )
42 
43 :end

用mplayer從視頻中按周期提取幀