How to convert a video without wasting file size and reducing quality?

[tendra]

I've been converting almost any kind of video into avi format and recently i have notice that some part of the video has different bitrate .For example ,to minimize wast of file size i use MEDIA INFO software to determine how much bitrate is it to convert into another format like avi but then again some part or the movie has more bit rate than it show on the software so in result that part of the video quality dramatically reduce .To prevent that i have to convert a whole video with ridiculously amount of bitrate .I'm using any video converter software free version and there is no auto bit rate detecting system so how should i fix it without wasting file size and video quality.

[Baldrick]

Try another converter and set the encoding mode to constant quality or 2-pass like handbrake, xvid4psp, WinFF.

[jagabo]

Use constant quality encoding. You get exactly the right bitrate at each and every frame to deliver the quality you specify.

It makes no sense to use the same bitrate as your source unless you are using the same codec and the same settings. In which case there's no reason to be doing the conversion.