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08.18.2008 at 07:28AM PDT, ID: 23656417
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7.5

TMemoryStream, TFileStream how to use them properly for big files.

Asked by panJames in Delphi Programming

Tags: ,

Hello Experts!

Two questions:

1. why does it take ages and crashes at the end?

procedure XYZ;

var LMemoryStream,
    LMemoryStream2 : TMemoryStream;

begin

  LMemoryStream := TMemoryStream.Create;
  LMemoryStream2 := TMemoryStream.Create;

  LMemoryStream.LoadFromFile('C:\MyFile.avi');  //80MB

  LMemoryStream.Seek(0, soFromBeginning);
  LMemoryStream2.CopyFrom(LMemoryStream, LMemoryStream.Size); //takes ages!


  LMemoryStream2.SaveToFile('C:\Result.avi');

  LMemoryStream.Free;
  LMemoryStream2.Free;

end;

2. I have a file. It's structure is:

[header]
2 bytes -> amount of images within (integer)

[offset table]
8 bytes -> position of first image (int64)

8 bytes -> position of second image (int64)

8 bytes -> position of third image (int64)

[images]

        -> first image
         
        -> second image

        -> third image
 
        and so on...
 

my task is to update selected images and rewrite a file.

The problem is that if updated image has got another size then original then every "N indexed"

image changes indexes on offset table from (N + 1) position and also moves all images on its right to the left or to the right...

I tried to use CopyFrom function but it takes AGES and does not seem to be working fine for 80MB stream.

What is the best approach to deal with this problem?

panJames



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[+][-]08.18.2008 at 08:48AM PDT, ID: 22252966

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About this solution

Zone: Delphi Programming
Tags: Borland, Delphi
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Solution Provided By: ciuly
Participating Experts: 2
Solution Grade: B
 
 
[+][-]08.18.2008 at 08:49AM PDT, ID: 22252979

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[+][-]08.18.2008 at 10:47AM PDT, ID: 22253938

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[+][-]08.19.2008 at 02:21AM PDT, ID: 22258219

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