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vishnubob / python-midi

Python MIDI library
MIT License
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Cannot find BPM change event #97

Open TheMariday opened 8 years ago

TheMariday commented 8 years ago

Hi there,

I can't seem to find the connection between ticks and ms.

I've got a few midi files with variable BPM's and I can't seem to see any BPM change events when inspecting the track data.

I've got it working fine when I know the BPM before hand, but if this is hard-coded in then I can only play songs with that specific BPM.

Thanks and looking forward to hearing back from you,

Sam.

MaurizioB commented 8 years ago

Are you completely sure that the BPM changes and it's not just that the notes have different time intervals?

vishnubob commented 8 years ago

I like that hypothesis. The only way to tell for sure is if we can examine a MIDI file.

TheMariday commented 8 years ago

Looks like I've figured this one out (sorry for pulling you in on this one!)

All my midi's are 120bpm. Ableton Live seems to have ZERO ways to export bpm or bpm changes with the midi file. Very very strange...

I'm gonna have to ditch all my songs with a variable BPM and input each songs BPM at command line.

Hey ho but thanks for the quick response.

Sam.

vishnubob commented 8 years ago

Another approach would be to use references like bass drums etc to figure out the downbeat, and then to re-write the entire pattern with tempo changes. It would require some heuristics, and re-writing of all tick offsets, but it should be possible.

MaurizioB commented 8 years ago

Well, while heuristics would be interesting, the best solution is to take note of tempo changes, delete all of them, export again, and write a simple script that adds tempo maps to the new imported files using python-midi.

vishnubob commented 8 years ago

I think the point is his track doesn't have tempo changes. Tempo maps are an invention of python-midi, and they rely on tempo change events. I don't think you could ever write a fool-proof algorithm that could infer tempo changes when there are no tempo change events. ie. I suggested heuristics because not because it's interesting, but because it's probably the easiest way to solve the problem of re-creating that information.

MaurizioB commented 8 years ago

Sorry, I meant Tempo Events. My solution was more a by-hand one: once you know when (in bars/pulses) a tempo change occurs, you export the track after removing all the tempo changes in it, and manually add them to the track using python-midi. Anyway, it amazes me that Live can't export tempo changes!

TheMariday commented 8 years ago

It boggles me that live doesn't support this. Even if you re-inport the midi back into Live it still just defaults to 120 bpm...

I think I'm gonna make note of the bpm and the changes then add them in with a script. Or use a different midi sequencer because this is getting silly. Probably gonna switch over to cubase or fruityloops.

Thanks for everyone's input and I'd love to share my project with you when its done.

vishnubob commented 8 years ago

thinking this through, i bet ableton converts MIDI tracks into its own internal timekeeping time structure. ableton tracks use INSANE resolutions in their exported MIDI tracks, which is probably a reflection of its internal resolution. of course ableton tracks tempo changes, it just doesn't export them as MIDI because, well, that's not really ableton's wheel house (exporting MIDI files). i'm guessing the problems of exporting MIDI from their internal structures are non-trivial.

TheMariday commented 8 years ago

Are you suggesting extracting the bpm from Abletons internal structure? That would be a challange,

In the meantime I've switched over to fruityloops. Still gobsmacked that it doesn't support this...