I’m not sure if this is a bug. But when I use H.264 Lossless Preset. When I go in the Advance tab and lower the quality from 100% to 85%. The exported file size increases by a massive amount. I would of thought it would decrease it? This occurs using the Stable release Shotcut 19.04 and also the Beta release Shotcut 19.06. I made a video unfortunately my mic was not captured in the video, so no sound sorry.
If this is known or has been reported already, I apologise. I tried searching here but couldn’t find a thread on it.
It is normal that often the output size is greater than the source. 85% is a high value for H.264 or HEVC. I see you are using NVENC hardware encoder, and I do not think this supports the lossless mode of H.264. So, it probably reject some option provided and returned to some default that is lower than 85%. We do not have logic that validates every combination of parameters in Export > Advanced especially in conjunction with every implementation of hardware encoder.