[pawel]

Have in mind that Youtube always re-encodes uploaded video. To maintain most of the original quality you need to prepare your file as close as to Youtube video encoding specification. You need to prepare only the highest quality/resolution version, and YT will add lower quality variants.

Except hundreds of ordinary video converters, unfortunately there is not much choice of good H.264 editors, especially freeware. Assuming Windows: You may try AviDemux and Free Video Editor. Almost unlimited possibilities offers AviSynth but it requires good knowledge of video encoding and a lot of learning of its scripting language. Commercial tools start from $70, like TMPGenc Smart Renderer, Video Mastering Works or Authoring Works.