AguirRe had a set of commands built in to pause rewind and FF demos.. haven't got around to asking him the how yet. 

JoeQuake has demo pause, rewind, fast forward.

Demo pause is an easy engine modification. Likewise, so is fast forward will more or less changes the timing of a frame similar to how host_framerate does or the FitzQuake host_timescale cvar does.

Demo rewind ... and I haven't looked at this code to think about it in 5 months or so (I was trying to get interpolation to work right in reverse. And I did (or at least so close the couple of remaining flaws would never be casually noticed). At least with everything except dynamic lights fade timing.) ...

But if memory serves correctly, it builds a stack of locations that point to the demo read positions of the previous demo frames within the demo. So to play in reverse, instead of going forward it picks the previous location from the array and uses that. And if there is no previous location, you are at the start of the demo.

You also have to create an extra "client time" storage unit because cl.time is still important for things like sounds ... you cannot play sounds in reverse so they still need to end after X seconds and only a "forward-only" time instance can do that. In fact, this is also true of particle animations and some other things. But there is also the "demo neutral time" that can go backwards and this should be used for reversible events like animation interpolation, movement interpolation, the display of the clock if you press TAB to see the true time in the demo, etc.

Also, by looking at the current demo read position and comparing against the length of the demo file, you can estimate the percent of demo playback to show a demo progress bar (!!!). 

Start the engine with "-fitz" option restores playtime in statusbar, among a few other things 

I never understood why the game time display was removed from QS. It's fairly useful, unlike the skill display. This would be better off as a console setting instead of a command line switch.

aguirRe's demo script was an alias config that had the cursor keys increase or decrease host_framerate by by 0.1 steps. No rewind, only fast forward and slow motion. 

I ported JoeQuake's demo rewind code a while back. It was ... "fun".

I think that Fitz's host_timescale is an infinitely more sensible option than host_framerate for controlling demo speed, but of course it needs engine support. 

Some textures are still fighting a bit on certain maps, although gl_zfix is enabled. But this is noticeable only if they are viewed from the distance. Can gl_farclip fix this if it's set to a ridiculous level, or parhaps some other gl_ trick? 

A high value of gl_farclip will make it worse as it reduces your z-buffer precision; ideally setting it low will help more (there is, of course, a tradeoff in that).

z-fighting is really a mapping problem, and it should be fixed in the map and not by the engine.

The traditional "fix" (using polygon offset) sucks because (a) the z-buffer is non-linear so offset factors will have different effects at different depths, and (b) the OpenGL spec allows polygon offset to be implementation-dependent, so the same offset factor may have different effects on different hardware. 

I haven't requested this (yet) but with Peg's RMQ demo's it'd be very useful. There's lots, and the level length is 30 minutes average.

And yeah, z-fighting is bad level building. 

What are the engines that can play and rec demos with reloads and map changes except DP? 

well... technically all of them.

save a game
die somewhere
type disconnect
type record demo
load a game

same for level transitions.
change level
save
type disconnect
type record demo
load the game and continue playing

this is extremely helpful when sending in beta demos! :) 

yeah... this is extremely awkward, hence I'm looking for engines that can do it seamlessly 

Engine tutorial: Playback demos recorded across map changes. (Ridiculously easy).

http://forums.inside3d.com/viewtopic.php?t=2397 

I haven't requested this (yet) but with Peg's RMQ demo's it'd be very useful. There's lots, and the level length is 30 minutes average.

Oh, you've already had this available for years. cl_demospeed; set to negative numbers to rewind; it fucks with the motion blur though so you may wish to disable that. 

just added support for this to quakespasm:
http://quakespasm.svn.sourceforge.net/viewvc/quakespasm?view=revision&revision=604
... in the svn repo now, will be part of next version 

There's a way to fix demos recorded across map changes, but it only works for protocol 15 and 10002. With BJP's convdem tool, simply append a short newly recorded demo snipped to the end of the existing one (merge) and the post-mapchange recording will be shown fully. 

.. yes it does: tested with this one:
http://quakespasm.sf.net/tmp/tt2.dem 

That's a really useful feature, .exe please? 

here: http://quakespasm.sf.net/tmp/quakespasm_exe_r604.zip 

Works on map change and map restart(after death) but doesn't work on loading a save. 

Host_Loadgame_f() normally does a CL_Disconnect(), therefore loading a save stops the recording as very much expected. 

Same for me, "Host_EndGame: Server disconnected". 

as I said, that is the normal course of things, and also is out of the scope of the fix I applied which touches playback code and not recording code. you guys really want to record demos by loading saves while in the middle of recording?? that can be tricky, I guess. (have anyone else implemented such a thing?) 

I like doing that. Make sharing or recording playthroughs much easier if you just record and forget. 

DP has it, but it uses different format\protocol 

i.e. demo recording continues until an explicit "stop" command