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Grimm

Megademo

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I know there's a commmand line parameter in Doom 2 somewhere that let's you set the size of the demo. My question, aprroximately how bytes are equal to one minute of a demo?

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-maxdemo

I usually use 1024 for recording. I've never recorded anything too big so that value works fine.

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I wonder what the actual limit to this is?
sometimes it lets me load it with -8192... but normally 4096 is as high as it will go. hmmm... Myk? RjY?

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RTDscout said:

how bytes are equal to one minute of a demo?

Doom records 4 bytes for each player in the game, every thirty-fifth of a second. So a minute woul d be 4*35*60 = 8400 bytes (multiplied by the number of players in the game) To put it another way, one megabyte of demo buffer would be 1048576/8400 = 124.83 minutes, over two hours, plenty of time for all but the largest maps.

This will probably be different for those source ports which have their own demo formats.

Opulent said:

I wonder what the actual limit to this [/b][-maxdemo][b] is?

The first thing I discovered when looking into this was PRBoom doesn't even have the parameter, it just records straight to disk. That's the speed of contemporary hardware for you, I guess.

Anyway, when you do -record <demo>, Doom claims a buffer of size -maxdemo kilobytes (defaulting to 128K) from its internal memory pool. According to the original source release, the size of this pool defaults to six megabytes. Given other data the game needs to have in memory, a maximum demo buffer size of four megabytes seems reasonable.

NB The original source release also mentions a .cfg file parameter called mb_used with which the memory pool size can be varied, but I can't find any evidence for this in the DOS executables... Might invalidate everything I've just written, but, it seems to fit the evidence, so...

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thanks RjY.
I've been working on HR30max -- the longest I've done is a mere 3 hours or so... but if I got anywhere near successful it would be much longer.
I estimate map20 would be completed(by me) at the 5 hour mark... then comes the hard maps. :P
but you're right, the longest demo I know of is the hr30 on the DSDA...

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