Apart from the 16 channel aspect, some of which is just down to the way the general midi is played not because you need 16 simultaneous notes played at exactly the same time in all cases...
MIDI channels have nothing to do with the the number of notes that can be played simultaneously. A single MIDI channel can play as many simultaneous notes as the hardware allows. All the channel does is define a set of parameters that apply to all notes played on that channel. Those parameters include the current patch (instrument) overall volume, stereo position, modulation (vibrato), pitch bend, effect send (reverb, chorus whatever) and various other parameters, depending on the hardware.
So, a MIDI piece that uses only one MIDI channel, say a piano composition, may suddenly play 8 concurrent notes whilst 4 more are still sustaining. That would require 12 audio channels on the Amiga to reproduce if you had to do it using only discrete single note samples.
Of course, if you were writing this for a tracker to start with, you'd find all of your commonly used chords first and prepare samples for them so that you can use a single channel.
it is very possible for Amiga to play back these tunes technically. DMCS was very early in the life of Amiga but around the time of the A1200 EA did release a sequel, although I doubt it has the general midi instruments available to play them without any hardware as you say.
I've seen software that'll rip the samples used for soundblaster GM sets and the like.
Memory for holding the samples is the issue, but essentially things like Startracker and other 8-channel MOD players for Amigas prove that technically it is possible to do more or less the same thing, in fact MOD is a superior technology given you pick the samples anyway.
2->1 channel mixing for 8-channel replay has many limitations though. The mix mode of OctaMED SS is far better, but you need more horsepower.
After all what is a MOD player doing, the same thing more or less. 50mhz 030 is enough to play an MP3 on the fly
That's debatable. It depends on the file and the quality settings used. You won't be playing back a 256kbps 44kHz stereo file at 14-bit through paula with that. Not without converting it to PCM first. Of course, you could use a hardware mp3 decoder, then even a 68000 is enough.
so I see no reason why you need that kind of power to play general midi music files, I could convert that youtube video I linked to an MP3 and just play that back too then.
I have MIDI compositions that have up to 64 notes playing concurrently. A vanilla 68000 simply cannot mix that many sound channels at an acceptable rate.
Anyway I need it as a MOD file for some other project, so looks like it's going to have to be a lot of manual experimentation and messing about trying to save out samples from other sources tacked onto a general MOD that exists already. Even so, the midi instruments are still not quite as good as the original ones, and I'm starting to wonder if there is a utility for ripping samples from MAME ROMs.....now that would be a really cool thing to do, and I think it is possible from some distant memory.
OctaMED SS can load SMF0 and SMF1 files and gives you a fair amount of control over how it should import them. If you want to convert a .mid file to a tracker format, this is a way to start.
