I have been experimenting with trimming video files in both VLC player using the recording feature to record a segment of a .mp4 or .mts clip and it saves a new clip without it exporting anything. It takes seconds vs exporting a clip in Premiere Pro CC. Also, in Windows 10 Movies and TV app it has a built in trim feature that just had sliders to trim a video and save it as a new one without encoding it. I'm guessing this doesn't reduce the quality but mantains the same quality as the original file?
I even went into premeire and used blend modes difference and stacked the original clip against the trimmed clip and see no artifacts or pixels showing through and I have the program monitor in premiere outputted to a 20 inch Monitor
its possible it can stream uncompressed. the best way to check difference mode is apply heavy contrast to both clips before difference mode as our eyes may not see 4:2:0 color recompression hidden in low luminance values; or better yet, a RGB pixel sampler.