Newbie question... my original video file was created with a Canon camera, 1920x1080, 30p. Codec: H.264/AVC/MPEG4.
I made a few small edits in Kdenlive (ver 0.9.. To render, I used HDV (1080, 30p). It takes about 20 minutes to render a 23-minute clip. This is very good. But the resulting file size was double the original (over 4Gigs).

Any suggestions on keeping the best video quality, but keeping the same file size and speedy rendering time?

Thanks.

Size vs quality is balanced by bitrate parameter in CBR, try to half this to half your final size. Depending on the video content a low bitrate can be sufficient to get high quality. If you used the latest 0.9.10 you could use constant quality settings, that would give you the min file size for the quality you ask...

Speed vs quality (CBR) or vs size (VBR) is tuned by x264 presets : there is a ultrafast tuning that skips all the refined compression options.
One trick for very large projects : with hundreds of source media Kdenlive may saturate RAM (due to thumbs in project view etc) and start to work with swap, extremely slow. So to render it in best conditions, select script option in render dialog, close Kdenlive and launch the script from command line.

Some hardware offer H264 encoding with higher speed, but this is not supported in FFMpeg (supports only for decoding, useful only to save bettery while watching a film, not for video work) so in MLT. Gstreamer recently added this support but not sure this is very reliable yet (and you have to export in several steps, so the time gain is not obvious)