I'd say the main difference is the bitrate because usually both files are h.265. The smaller files have bitrates of max. 30 Mbps, while the 'original' can go up to 200 Mbps.
In case of non-SLR studios, the original file is the file that the external studio provides. If studios have their own website, it is usually the highest quality file that you will get there if you have subscription.
SLR is reducing the sizes of original files and I understand they do it to reduce traffic and to ensure a good streaming experience. There seem to be two rules to how they reduce file sizes:
- Any file with bitrates up to 75 Mbps will be reduced to approx. 40 % of its original size. So if the original video has 50 Mbps, the SLR reduced size version will have a bitrate of 20 Mbps.
- Any file with bitrates higher than 75 will be downsized even more to reach the max. allowed bitrate of 30 Mbps. So if the original has 120 Mbps, it will be reduced to 25 % of its original size to reach 30 Mbps.
One thing I do not get at all is why SLR insists to reduce 50 Mbps files to 20 Mbps instead of making all files 30 Mbps. 20 Mbps will lead to significantly inferior quality.
One example:
https://www.sexlikereal.com/scenes/7sins-greed-36359?tab=downloads
- Original is 50 Mbps
- SLR reduces file size to 42 % (from 17.36 GB to 7.34 GB), resulting in a bitrate of approx. 21
- To ensure better video quality, SLR could reduce only to 30 Mbps, resulting in a 10.4 GB file.
I think there is absolutely no need to substantially decrease the quality of 50 Mbps files which are already relatively small just to save 3 GB of traffic which is nothing in the grand scheme of things. But that's how it's done.
