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I have downloaded some clips from the net that were split into several files. There are 8 files and they are exactly 130 MB in total.

There are 8 files in .WMV format 130 MB in total

Now I use merging software that can also convert the files into different formats. Ill give you a small table of what happens when I merge the files.

130 MB .wmv -> 285 MB .wmv
130 MB .wmv -> 401 MB .avi (DivX)

So my question is what happens to the file, why is the output file so different from the original size. Does the DivX have some better quality or something. I thought it was impossible to go higher in quality from a low quality file.

In all the file formats the video quality is a bit jittery.

On a sidenote
Can anyone recommend some good software on merging the files. When I use this software the audio and video becomes out of sync

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up vote 0 down vote accepted

You can upconvert video, it doesn't increase the quality but it does increase the size. If there's nothing of equivelant quality or higher for it to resample it can't create "better" quality. You may want to chose a format which has lower quality if you need a smaller file size.

As for a video program which does this kind of stuff: VideoDub was awesome last time I used it.

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Thank you I will look at VideoDub. Do you have any idea why the size increases, what is stored in a file that is the same quality but almost 3 times as big. –  Saif Bechan Jun 23 '10 at 1:30
    
Different formats encode in different ways. If you took an MP4 format and compared it to xvid or H.264 of the same quality the MP4 would be much larger. It's just how effective the compression and algorithm is. –  Daisetsu Jun 23 '10 at 16:53
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