Just before a level begins, there is a slight freeze when the world name and planet appear and the level starts. It looks like its changing the resolution or refresh rate causing the brief freeze. Then the level starts and everything is fine.

Is there any way to stop this from happening without having to use the SVM build of dosbox?

EDIT: I should specify this is for Jazz CD.

Yeah I have the same, it's not game breaking just an annoyance.

I got this to stop by going into the folder, editing dosbox_jazz.conf so that output=opengl and scaler=none

i don't know why gog so often uses the settings they pick for dosbox games, they could be optimized better.

only problem i have now is a bit of vertical sync tearing, but it looks nicer so I'll put up with it.

Hm, that seemed to make things worse for me. The sound gets all messed up and everything is like 3 fps in any mode other than overlay. Strange.

I had the same issue with the start of levels freezing for about 3-5 seconds. I don't know where I found this fix but it worked for me:

in the game directory open up dosbox_jazz.conf with notepad

find the [cpu] configuration section

change the line cputype=auto to:
cputype=pentium_slow

this fixed the freezes for me, I've also swtiched the default dosbox to dosbox ECE but it worked even before I did this.
hope it helps.

dosbox ECE seems to work quite well actually, thanks mmodri. The only issue is I have black bars horizontally as well as vertically. I'm sure its an easy tweak in the config but I can't seem to find it. Do you know any way to have it 4:3?

in the dosbox_jazz.conf file:

windowresolution=1024x768 < set to whatever 4:3 resolution you want (or fullresolution if using fullscreen)
then set aspect=false under [renderer]

you might need to use output=ddraw or output=surface so it doesn't force pixel perfect scaling in Dosbox ECE.

let me know if it works for you as I can't test it right now.

Got it, thanks again.

Bad idea. The game actually runs at 8:5(Or 16:10, if you want to be wrong. :P), while only the menus, planet loading sequence, and some other small pieces run in 4:3.

That's actually why the freezes happen; the game is switching between its two resolutions of 320x240(Menus, the planet zooming in space) and 320x200(In-game, "Now approaching" text). Get it to just use one, or play in a window, and you'll be golden.

you are correct, and most DOS games play in 320x200 mode, but were made to be stretched to 4:3 CRT's at the time, so by forcing it to not scale it's actually closer to what the intended experience is, I prefer playing it in pixel perfect scaling and not forcing it to a specific resolution, I was just answering his question to force it to 4:3.

Jazz Jackrabbit actually doesn't use the common 320x200@70hz DOS mode. It runs at a custom 320x199@60hz mode. Unlike all other similar DOS games (which are 4:3) it might actually have been intended to run at 16:10.

It was definitely intended to run at 16:10.
As for 320x199... I'm not sure it was intended to run at that resolution; I've heard it's a bug in DOSBox. Allegedly, it should output at 320x200, probably at 60hz, but DOSBox interprets its odd way of addressing the VGA adaptor as being 320x199.

Why do you think so?

Some of the graphics looking correct at 16:10? That means the artist was working on a 1:1 PAR display, but that doesn't mean the game as a whole was designed for it.

That it's the way it would display on a CRT? Is it really? Most people would change their monitor settings to fill out a screen rather than assume a DOS game was widescreen.

I mean it's a very good assumption, but you can't say anything for sure about these old games. Unless you have a developer interview (which would be very interesting for this title).

Actually owning a physical copy of Jazz Jackrabbit CD and having semi-recently run it on a Windows 98 machine hooked up to a CRT: yes, it runs at a comparatively widescreen aspect ratio compared to the main menu and "Now Entering [Planet]" screens. Adjusting your monitor for this would entail adjusting it every time a stage loaded and then adjusting it back when you returned to the main menu (because the top and bottom of the screen would be cut off when it went back to that resolution), so it'd hardly have been worth the trouble.

Don't CRTs remember different settings per resolution (sorry it's been a long time since I've owned a computer CRT)? Have you tried it? Because that would be interesting.