I am new to kdenlive. I see references to libavcodec-extra-54 (for Trusty). Is there something to gained from installing it? For example, I am running on an old rather slow computer that sometimes can't keep up with videos.. Is there a libavcodec-extra-54 codec that would speed things up??? Is there some other reason that I should have the extra codecs???

For slowness turn on proxies https://userbase.kde.org/Kdenlive/Manua ... roxy_clips

I don't think libavcodec-extra-54 package offers better speeds. It just has extra video codecs. ie it means you can play back a wider range of video formats and encode into a wider range of formats. But the regular libavcodec54 seems to have all the codecs I need.