[PD] write tempo change with [midifile]?

[tim vets]

Hello,
I've been looking into writing out midi using mrpeach's [midifile].
Now I'm trying to write a tempo change message into the midi file.
So far I figured out that the message format should be "FF 51 tt tt tt".
(e.g. as described here http://www.deluge.co/?q=midi-tempo-bpm )
I'm not sure though, how to translate that into a message that [midifile]
can accept to correctly write the tempo change into the file.
I tried a few variations, like [255 81 500000( (for 120bpm)
or by first changing the 500000 into three hexadecimal bytes, and then turn
those into 3 floats
[255 81 7 51 0(
but all I get is extremely low tempi when I import that midifile into a DAW
(I seem to get the most informative results with Rosegarden)
Any ideas?
thanks!
Tim
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