Support Seek and other functions for fluidsynth 2+

[TheCycoONE]

Fluidsynth 2 supports:
Seek: https://www.fluidsynth.org/api/group__midi__player.html#gaab5fe5b25ff513919b138d77e079c75a
Tell: https://www.fluidsynth.org/api/group__midi__player.html#gabc2d114e2a6926f4db800286b2ebb1da
Duration: https://www.fluidsynth.org/api/group__midi__player.html#gab8bec2b53e07daf2313412e4663c0fa7

When Fluidsynth 2 is used, these functions should be available.

This would fix an issue for us where Mix_PlayMusic continues from where it left off instead of the beginning of the track: CorsixTH/CorsixTH#2328

[TheCycoONE]

While making these changes it might be worth hooking Play and Stop into Resume and Pause because in fluidsynth they are equivalent.

[slouken]

That sounds like a good idea. Do you want to submit a PR?

[TheCycoONE]

I wouldn't mind but it may be awhile before I have time. If someone else beats me to it I'm just as happy.

[joanbm]

Hmmm, there's a problem with PR #521 in that FluidSynth's ticks are not milliseconds.

For example, with this MIDI file, Mix_MusicDuration will return a false duration of 3 seconds since FluidSynth's fluid_player_get_total_ticks will return ~3000 ticks, while the actual duration is about 8 seconds long.

Some more information can be found in this issue: FluidSynth/fluidsynth#1151. The TL;DR is that FluidSynth deems reporting duration and seeking in milliseconds to be out-of-scope.

[sezero]

Well, just tried it, and playmus program reports wrong position and 0 duration for a midi file I tried. So there is definitely something wrong with the patch. And I don't know fluidsynth much to offer a solution. @TheCycoONE ?

[joanbm]

Well, just tried it, and playmus program reports wrong position and 0 duration for a midi file I tried.

The '0 duration' problem may be because FluidSynth's fluid_player_get_total_ticks returns 0 until the playback actually starts. See FluidSynth/fluidsynth#648.

A simple hack I found for this issue is that if after calling fluid_player_play, you call fluid_synth_process(synth, 1, 0, NULL, 0, NULL);, then fluid_player_get_total_ticks will return the right value. Though that's pretty much useless for us because it's measured in ticks, not milliseconds.

So far I haven' t been able to find any good way to translate ticks ↔️ milliseconds using only FluidSynth. As far as I can tell, it can be done by registering a callback using fluid_player_set_playback_callback to listen for "set tempo" events (i.e. fluid_midi_event_get_type(event) = 0x51), then processing the entire file using fluid_synth_process to get all events, but performance is not great since this triggers a lot of the logic for rendering a MIDI to an audio buffer.

For my similar use case I'm looking into using libsmf in addition to FluidSynth to deal with this problem more cleanly.
For SDL2_Mixer I think it should be possible to use/adapt the already built-in libtimidity to do it, or to try to contribute a feature upstream in FluidSynth.

[sezero]

I'm afraid it'll turn out to be way too much trouble than it's worth and we'll have to revert the patches

[slouken]

I agree, let's revert the initial commit and this can come back as a new PR once everything is ironed out.

[sezero]

Patch reverted from both SDL2 and main branches. That reverted the FLUIDSYNTH_Pause and FLUIDSYNTH_Resume additions too: if we do really want them, one should hand-pick them and put them back.

[joanbm]

Yeah, I think that the right place to do this is in FluidSynth itself. And I don't think it's that complicated (famous last words?), since FluidSynth already has all the necessary pieces internally.

• Tell can be done by exposing this property, I think.
• Duration should be doable similarly to the total ticks code, but keeping track of the current tempo along the way by looking for events of type MIDI_SET_TEMPO .
• Seek can also be done with the same iteration logic as Duration, but breaking after you find the first event with a timestamp >= desired time. Then you call fluid_player_seek of the corresponding ticks for that event.

[TheCycoONE]

The main thing I was going for was resetting the track on Play and supporting Pause/Resume.

My understanding of https://www.fluidsynth.org/api/group__sequencer.html#ga7f48dab4cde18da6e0fa76458849c19a was that ticks defaulted to ms but I admit I didn't test that aspect and reading more I see I was completely mistaken. Seek 0 on play is still useful though.

[slouken]

The main thing I was going for was resetting the track on Play and supporting Pause/Resume.

Feel free to resubmit a PR with just those aspects implemented.