获取AVI文件持续时间 [英] Getting AVI file duration

问题描述

我正在写的代码是用于搜索用户驱动器和检测warez（注意：决定是否有一些文件是否合法是超出了这个问题的范围）。我们做MP3，WMA和一些图形文件搜索。现在我们想检测非法电影。我想打开AVI文件，从中读取一些细节并关闭它。我有以下代码：

 使用WFV; // from JEDI api wrappers 
 
 procedure TForm1.Button1Click（Sender：TObject）; 
 var 
 lInfo：TAVIFILEINFOW; 
 lFile：IAVIFILE; 
 lFileType：string; 
 lLenMinutes：integer; 
 lFPS：integer; 
 begin 
 {init file} 
 AVIFileInit; 
尝试
 {打开文件 - 注意：因为我们搜索warez这是完美的warezy文件} 
 AVIFileOpen（lFile，'e：\Sideways KLAXXON\Sideways KLAXXON.avi' ，OF_READ，nil）; 
尝试
 {获取文件信息} 
 AVIFileInfoW（lFile，lInfo，sizeof（lInfo））; 
 lFPS：= Round（lInfo.dwRate /lInfo.dwScale）; 
 lLenMinutes：= Round（lInfo.dwLength / lFPS / 60）; 
 lFileType：= lInfo.szFileType; 
 {只是为了展示：准备一些备忘录，看看我们得到什么} 
 memo1.Lines.Clear; 
 memo1.Lines.Add（'文件长度[min]：'+ IntToStr（lLenMinutes））; 
 memo1.Lines.Add（'Width：'+ IntToStr（lInfo.dwWidth））; 
 memo1.Lines.Add（'Height：'+ IntToStr（lInfo.dwHeight））; 
 memo1.Lines.Add（'文件类型：'+ lFileType）; 
 finally 
 {关闭文件} 
 AVIFileRelease（lFile）; 
指针（lFile）：= nil; 
结束
终于
 {发布库} 
 AVIFileExit; 
结束
结束
  

所以lLenMinutes是等于98，而电影大约121分钟。这是一个巨大的区别。我究竟做错了什么？ dwRate是100万，dwScale是40k，所以FPS是完美的25.dwLength是147k MSDN说：单位由dwRate和dwScale定义。

注意：这是一个从这个问题的跟进，但是由于崩溃的问题已经解决了，我关闭了另一个问题，并在这里提出了改进的内容。

解决方案

MSDN表示 dwScale 成员 AVIFILEINFO ：

任何流都可以定义自己的时间标度来取代文件的时间尺度。

您确定流不会覆盖 AVIFILEINFO 结构中给出的速率和比例吗？流的速率和比例存储在 AVISTREAMINFO 结构。

I am using VFW unit from JEDI wrapper on WinAPI.

The code I am writing is intended to search user drives and detect warez (note: deciding if some file is legal or not is beyond scope of this question). We do MP3, WMA and some graphic file search. Now we want to detect illegal movies. I want to open AVI file, read some details from it and close it. I have the following code:

uses WFV; //from JEDI api wrappers

procedure TForm1.Button1Click(Sender: TObject);
var
  lInfo : TAVIFILEINFOW;
  lFile : IAVIFILE;
  lFileType : string;
  lLenMinutes : integer;
  lFPS : integer;
begin
  {init file}
  AVIFileInit;
  try
    {Open file - note: since we search for warez this is perfely "warezy" file}
    AVIFileOpen(lFile, 'e:\Sideways KLAXXON\Sideways KLAXXON.avi', OF_READ, nil);
    try
      {Get file info} 
      AVIFileInfoW(lFile, lInfo, sizeof(lInfo));
      lFPS:=Round(lInfo.dwRate /lInfo.dwScale);
      lLenMinutes := Round(lInfo.dwLength  / lFPS / 60);
      lFileType := lInfo.szFileType;
      {just for show: prepare some memo to see what we get}
      memo1.Lines.Clear;
      memo1.Lines.Add('File lenght [min]: ' + IntToStr(lLenMinutes));
      memo1.Lines.Add('Width: ' + IntToStr(lInfo.dwWidth));
      memo1.Lines.Add('Height: ' + IntToStr(lInfo.dwHeight));
      memo1.Lines.Add('File type: ' + lFileType);
    finally
      {Closing the file}
      AVIFileRelease (lFile);
      Pointer(lFile) := nil;
    end;
  finally
    {Releasing library}
    AVIFileExit;
  end;
end;

So the lLenMinutes is something equal to 98 while the movie is about 121 minutes long. This is a huge difference. What am I doing wrong? dwRate is 1 million and dwScale is 40k, so the FPS is perfectly 25. dwLength is 147k MSDN says: "The units are defined by dwRate and dwScale".

Note: this is a follow-up from this question, but since the crashing problem has been solved, I closed the other question and moved improved content here.

解决方案

MSDN says for the dwScale member of AVIFILEINFO:

Any stream can define its own time scale to supersede the file time scale.

are you sure the streams does not override the rate and scale given in the AVIFILEINFOstructure ? the rate and scale for a stream is stored in an AVISTREAMINFO structure.

这篇关于获取AVI文件持续时间的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！