That’s a bit passive-aggressive,
I converted this site from Blocs when it as around 200 pages. The project file was around 100MB, because all its assets are held externally. Unfortunately, each release introduced as many bugs as it fixed.
I always thought this community was for discussion and assistance. I asked for advice or “hacks” to reduce my project file size. Maybe you should give a thought to how you decide to offer your help.
No they are stored in the cache, on your Mac. You can see the cache disk space usage from the Sparkle Preferences. Clearing the cache regenerates it at the next publish.
Duncan,
I’ve accepted that the size of the file is what it is. My opinion is that a little more could be done to compress poster images (which seems to be my main issue). However, reducing the project file size is a “wishlist” thing. It’s annoying but it’s not mission critical.
So, thanks for your interest and thanks to many other community members for coming up with ideas. I think this topic has run its course, and I’ve learnt a number of things along the way.
Regards
John
How are poster images affecting the file size? How can I reproduce it?
First a copy of my reply to Matt (11 hrs ago)
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Re-reading your note, I had an idea. I used an ftp program to download the “Images” folder from the published site. It contains 267MB of files. My guess is these are stored in the project file, rather than being generated each time during publishing.
Most of the filenames begin “poster”, suggesting these are badly compressed stills for the 305 videos used on the site. I’d resorted to using video because of the amount of space used by galleries storing images (at one time my project file had exceeded 2GB!!!).
So… Nothing I can easily do about it. If a project contains lots of images or videos, project file size is something to live with. Unless, of course, someone has a suggestion 
.
Just for fun, I loaded the largest poster (999MB) into an editor, made no changes and saved it at 100% jpg quality. The resulting file size was 378MB. A webp version at 80% was a mere 84MB. Interesting?
Once again, thank you (and others) for trying to assist.
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It appears that for each video file a poster image is created. Logical, because there has to be a still before “play” is pressed (and Sparkle allows you to select the frame). The reply to Matt examined the uploaded files to the website server.
If (my assumption) these poster are also stored in the project file, they’re far bigger than they need to be in terms of jpg compression. My site has a hell’ve a lot of videos!
Hope that helps.
Ah nice catch, looks like the poster image is being stored uncompressed. Changed that for 4.0.5. Unfortunately it’s not that simple to compress poster images in existing project files, but newly added videos will get a compressed poster image.
I tested with a blank project and and a video not stored in the project file, so the file was a single poster image alone. This went from 8.3MB to 382KB.
Two possible ideas
Use the “Replace” option to remove the video and then replace it with the identical video.
Change the poster image selected for each video. A new poster would need to be generated.
Do you think either might work?
Honestly, that was in no way passive-aggressive meant. Apologies if you cannot handle my german humour.
You don’t need to take my offer for help and there is always a block option if you need it. 
I think if you read Duncan’s response you’ll see there was a problem and he’s fixed it.
@duncan Looking a little deeper, posters are generated for page background videos. Are these needed?
Maybe not, we’ll look into this but for a later update.