[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [fluid-dev] Patch for handling midi note events

From: David Henningsson
Subject: Re: [fluid-dev] Patch for handling midi note events
Date: Sat, 07 May 2011 21:21:10 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20110419 Thunderbird/3.1.9

On 2011-05-06 19:03, Pedro Lopez-Cabanillas wrote:

Sorry for coming so late to the discussion.

On Friday 06 May 2011, Jonathan Slenders wrote:
One thing, I moved player->user_callback(...)
before fluid_synth_handle_midi_event. Because I sometimes also wanted to
adjust the pan, the volume, and instruments on the channel played for a
I can also image that someone (maybe me too) wants to alter the midi events,
supress notes or change pitch an octave up at a certain point.

Me too :-)

Seriously. This is something that I was planning for using in one of my pet projects: http://www.kde.org/applications/multimedia/kmid . This program is a MIDI/karaoke player with features like pitch transpose, tempo control, channel solo/mute, synchronized lyrics display and integrated pianola. It plays to hardware MIDI ports or soft synths. The program has three MIDI backends right now: Linux/ALSA, Windows and MacOSX/CoreMIDI. My plan was to develop a fourth backend based on FluidSynth only. It would require exactly the same feature you are trying: a callback just before delivering the MIDI event to the synth, allowing the client application to change event's parameters. But for my program this is only one of the required additions to FluidSynth. Another one would be a callback while FS is parsing the MIDI file, reporting to the client application all the meta-events like titles, track names, copyright notices, texts and lyrics, time/key signatures, that are ignored right
w in FluidSynth but would be required by kmid. Talking about text and lyrics, 
these events would be reported by the player callback at playing time as well, 
although they would be ignored by the synthesizer.

Considering the two proposed callbacks, instead of new_fluid_player2() perhaps 
I would prefer two functions: fluid_player_register_playback_callback() and 
fluid_player_register_parser_callback() with their corresponding unregister() 

The parser callback would be quite innocuous in process time constraints, and 
will be called in the same thread as fluid_player_add(), so there is little 
concern about it. The playback callback is another issue: first, it will be 
potentially called from a realtime thread, with small time constraints. If the 
callback allows event modifications it should be called synchronously, ahead of 
the delivering time to the synth, and the client application would need to 
return within this time frame. It would be easier to implement a pure 
notification callback, called asynchronously from FluidSynth but without 
allowing event modifications.

Talking about events. The structure fluid_midi_event_t has been opaque for a 
long time in FluidSynth, and I think it should remain opaque. There are API 
functions to access some event properties, and more API functions would be 
welcome if needed.


Hi folks and thanks for the patches and comments,

I mostly agree with Pedro (e g about letting the fluid_midi_event_t remain hidden), but I'd like the callback function to be used instead of (rather than before or after) calling fluid_synth_handle_midi_event. That means that we'll start off with the player's callback function pointer being fluid_synth_handle_midi_event (for simplicity and backwards compatibility) but we can change it through a new api function called fluid_player_set_playback_callback(). That way you should be able to not only insert your own processing (eavesdropping, changing and removing notes as necessary), but also to insert our existing midi router into the playback chain for midi files.

Does that make sense or am I missing something?

(Btw - I'm holding a speech on FluidSynth real-time and thread safety challenges tomorrow morning, if you like you can listen and ask questions on IRC in real-time. [1])

// David

[1] http://lac.linuxaudio.org/2011/?page=program&mode=table&day=3

reply via email to

[Prev in Thread] Current Thread [Next in Thread]