Have you ever questioned that how media converter actually works to convert a media file to another format? Here are some useful information that I’ve collected from Wikipedia and other Internet sources.
Transcoding is the direct digital-to-digital conversion of one encoding to another, such as for movie data files (e.g., PAL, SECAM, NTSC), audio files (e.g., MP3, WAV), or character encoding (e.g., UTF-8, ISO/IEC 8859). This is usually done in cases where a target device does not support the format or has limited storage capacity that mandates a reduced file size, or to convert incompatible or obsolete data to a better-supported or modern format.
Transcoding is commonly a lossy process, introducing generation loss; however, transcoding can be lossless if the output is either losslessly compressed or uncompressed.
The process of transcoding into a lossy format introduces varying degrees of generation loss, while the transcoding from lossy to lossless or uncompressed is technically a lossless conversion because no information is lost; however, the process is irreversible and is more correctly known as destructive.
From other sources
“First it does not just change a setting, it has to recode the actual images of the video. How it does that varies greatly depending on the format and standard and options you want.
For a nearly perfect copy it works about the same as how a compression software like WinZip works, it looks for any data that is the same in an image and instead of duplicating it many times over, just does a quick math calculation that is an abstract of the actual image, then reverses it on playback. So something like RED RED RED RED RED RED RED ends up looking like RED x 7. You took that long string of color data, and changed it to one string of color and a math calculation on where that red should go.
For converters like DIVX they actually have to toss out information, how they decide what to discard and how they recode it so it looks decent at 1/5 the size if the original will take a very very long book.”
If you are looking for a good video converter software, you can check this list: