Rather that directly answer your question I think I'll just point out that this is probably a bad idea.
If you are converting between different codecs, this will involve not only a deterioration in quality but also potentially wasted disk space, since each codec has its own characteristics at a given bitrate. That is, it's possible to transcode from format A to B and have a larger file size but reduced visual quality. Transcoding between two different lossy compression algorithms will never improve the image quality, nor retain the same image quality, only degrade it by varying degrees. So it doesn't make sense to do such transcoding between formats unless the benefits outweigh this quality degradation.
I'd advise keeping the videos in their original format, and only converting them when there are significant benefits to doing so, such as:
When the videos are at a very high bitrate and you cannot afford the disk space; you want to use a significantly lower bitrate - in which case you don't care about the reduction in quality.
When the videos are in a format that is not supported by computers or devices you own or are in a "dead" format nobody is likely to use anymore - in which case the reduction in quality is unavoidable in order for the videos to remain compatible.
When you are outputting to a specific target, such as authoring a DVD disc - in which case the reduction in quality is again unavoidable.
In all other cases, why not retain videos in their original format?