What is a good efficient way to isolate clips from long movies? I am making a video that is an analysis of various films. My hope is to get clips from the movies to demonstrate various points I'm talking about.

I'm using Kdenlive on Ubuntu. One issue is that it seems like loading a whole movie length video slows it down making it hard to move around to the right frames (the computer is an i5 with 4GB RAM, so it's not a particularly slow computer).

The main problem, though, is that I want to select sections and edit them out so I can have them as clips ready to include in my master edit. However, if I go through the render process, I'll end up affecting the compression and video quality settings.

Is there a way I can specify a start and end point in hours, minutes, and seconds, and then output that portion into a new file, without changing the quality of the video?

Perhaps something at the command line? That way I could scan through the video using a more efficient player like VLC or something, and pick out my start and stop times there.

Additional note, in case it matters: I don't need the sound, just the image.
What format is your long video? The seeking performance problem may not be in Kdenlive but in your movie. If you aren't yet, you should consider using a container format that has index tables.

Now regarding extracting a clip from a movie, I believe you can do that with ffmpeg, specifying a codec named "copy" and setting a start position and a duration (in seconds):

ffmpeg -ss &lt;start-position&gt; -i &lt;source-filename&gt; -vcodec copy -acodec copy -t &lt;duration&gt; &lt;destination-filename&gt;