Question on Blu ray image size output and reducing the size

Question

Hi
I have been using encore for blu ray projects which is been proving very helpful. However recently i have had a issue with output size on files. Normally Encore gives me it's estimate that it will fill the disc nicely and provides a image/folder which is about 17-20GB (using 25GB disc) but now out of the blue it's files sizes it outputs has been 24.8GB which technically is less than 25GB but as anyone knows who burns to media, the disc doesn't actually have 25GB of space (something like 23,8 or something, i can't remember without checking). Anyway of course this is a issue because my output size is contantly now coming up to be about 600MB - 1GB over the disc actual size, i figured Encore normally compresses files to fit considering i have burned similar amounts/size media before and never had a issue.
Anyway my issue is the slightly larger file size, i figured the easiest way to reduce the blu ray output size was to of course play with the transcode settings, which usually are set to the default settings for Blu ray (the quality preset is called something like "1280x720p 50 High Quality MPEG-2") so of course i thought to lower the bitrate a little just for a test, so i did just that and cut the default bit rate from 25[Mbs] to 20, i didn't want to lower it too much as it was a test to see what i could save for file size. Anyway so i re-transcoded the file and built another image, sadly the image size oddly enough came out as 26.something GB... so it actually grew in size by reducing the file bitrate which put me at a loss. I was wondering what common ways i could use to lower this file size just by a few hundred MB or up to 1GB in this case without having to remove content from the disc (it would be a waste to not only seperate the content but to use a whole disc for a leftover 600mb-1gb project). I of course want to keep quality as high as possible but i understand when trying to reduce size quality has to normally be hit in these situations so i can deal with a slight loss of quality. I have been browsing the forums here and though some topics seem similar they have the issue of file sizes coming out as 40GB+.
Now im no genius with Encore, normally as said the file size is always between 17-20GB as i figure encore was using a "fit to disc" type feature but because the output size is technically below 25gb but not actually below enough to burn i was wondering 2 things:
1) is it possible to make encore it's self shrink these files a little more, lowering the target size down by 1GB would do wonders but only option i have seen is to have a 25GB disc or DL disc with no option to customize the output size (forcefully lowering it by 1GB).
2) because i imagine the above can't be done i was wondering how to go about reducing the size by around 1GB or so, i don't need like 10GB freeing up so it's only a small amount, as said this is a issue i have had with the last few projects i made and the size varies from needing 600MB - 1GB (it doesn't usually exceed needing 1GB free space... besides when i lowered the bit rate which increased size a lot). In the past i always just cut the bitrate of files down a little (never by lots but enough to free space up) but clearly that failed my test so im at a loss of how to reduce file size without a huge loss in quality.
For the record i have already produced the file as both a image file and a folder and both have the same issue.
Extra info on the project:
It contains 4 Menu's, 13 video files which vary in lengh from short ones at about 5mintues to longer ones which the largest is about 20minutes. I commonly burn this number of video files/space with fine quality and no issue so i would rather not take files from the project.
quality preset details are defaultly as said above set to "1280x720p 50 High quality MPEG-2" settings, i am not on my computer with encore at the moment so i can't post full specifics right now but if you have encore handy you should be able to check.
Tried reducing bit rate but that increased overall size, the actual plan was to hopefully lower the bit rate to around 21 [mbs] (from 25) and then do that for multiple (or all) files until it fitted but after it increased the size i lost hope there, it said the estimated file size (on the individual video) would drop by around 300-400mb  but that didn't work.
I have tried both folder and iso which always come out the same size.
Basically my main question/problem is any suggestion to drop the file size by up to 1GB without taking items out the project or a real high loss in quality (i don't mind small loss though as i can apply whatever solution to all files which should help).
Any suggestions what i can try? as you probably gather im not a genius when it comes to this stuff but i tried including what i thought is relevent.

Answer 1

Hi and thank you for the reply;
one problem i seem to be having when reducing the bitrate is the file size is oddly increasing from 24.8GB to 26.4GB, i can't really figure this one out as well it's having the oppisite effect. I checked the "streams" folder on output and decided to compare automatic transcoding to manual lowered bitrate and im not too sure where the increased file size is going, i found which video file it was causing the issue, all videos files range or average around 1.6GB each but one file was taking 4.5GB, after lowering that files bitrate it cut it down to 2GB which was of course saving me 2GB from the old file but the overall size had increased which was odd. Seems the other files are all the same so it hasn't tried improving them (so it seems) so i can't make ends of why the size is increasing.
I will try playing with the source file to see if i can do anything that way, if not i will try transcoding in premiere (i have had troubles with this before so i try to avoid it).
Oh and yes i was using Automatic.
Anyway i will see if editing the file outside might help first and see how that works. Thanks again for the reply.