I did new test this morning after my pc was rebooted and the conversion is ok now.
May be I did something wrong
Currently, I added timidity support into my local test build.
To make it easy to use, I load a config file under avxcat dir with timidity parms (except those required)
This may allow add parms to load an external timidity config file or add "s 44100" etc...
The single (I hope) command used may allow to convert midi into any other audio codec with ffmpeg help
It looks promising but I have to resolve one "needed missing information" I asked timidity author about howto get it... (midi estimated time without any conversion process)
Those been interested buy a test build as soon it is ready could send me an email with subject (avxcat - timidity test).
Kind regards
Remy