I am completely new to KDEnlive and video editing. However, having read a few articles I know have a file I wish to render.

The source file is a .ts file taken from Media Portal, the file size is 13GB. All I wish to do is remove 3 minutes from the start of this video clip. When I choose to render the file as 'Lossless 'HQ' 'H264.lossless fast' the output file is 14Gb after an hour with a reported 11 hours left to run! Why is the output file so much larger than the source file?

Surely there must be an easier (and faster) way to edit three minutes from this video clip.

Any help would be appreciated.

Kdenlive is a typical nonlinear video editor in that it is not for trimming an existing clip but for composing a new video from a bunch of clips, snippets from these clips, images, and so on. The final video output is always rendered and not simply copied over (think of different I frame positions in the output compared to the possibly multiple input frames, et cetera, that require new encoding).

For what you want to achieve you should investigate into ffmpeg, not Kdenlive. It allows to actually trim video without reencoding. However this comes at the considerably small price that you can't exactly control the cut or trim points. Ffmpeg will always use the next I frame in such a way that the part you are interested in is always included, but you typically get more frames than specified. For instance, see my blog about Trimming Video Files Lossless Using ffmpeg. This should give you the required information so you can trim your video footage.

To answer the question about the file size: File size primarily depends on the video and audio bitrate. Rendering lossless is rendering something like 240.000 kbit which produces approx. 30MByte output for each second of your movie. The downloaded file surely will have a bitrate far, far below and thus a smaller file size.