The problem is in the creation of the MIDI recording itself, not in the "export to audio file" feature.

Have you tried to run any tests with 5-pin MIDI DIN connectors along with a USB connection?  On macOS an older type serial connection might present more options to you than a newer USB one by itself does.

With my YAMAHA DIGITAL PIANO P-95 connected via 5-pin MIDI DIN connectors plugged directly into a MOTU Micro Lite (USB MIDI interface) I've got some which immediately I can check off the Yamaha Keyboard Properties window inside MIDI Studio of the Audio MIDI Setup on macOS.  They seem unavailable to direct MIDI device to computer connections made over only an attached USB cable alone.

MIDI Beat Clock and MIDI Time Code are additions available as properties I can check off that the keyboard transmits and receives, while General MIDI and MIDI Machine Control I can check off also but as features of the MIDI device whenever connected through 5-pin MIDI DIN connections.

Each of the designations show under Transmits and Features and has a check box so long as I'm making the adequate connections on MIDI serial cables with their MIDI DIN connectors.

I’m saying this to say that MIDI Beat Clock and MIDI Time Code, both available to anyone using 5-pin MIDI DIN connectors, also might alleviate some of the MIDI timing problems you experience.

If everything else is correct I would suspect a sampling rate issue there (something other than 48 kHz).

I have experienced that issue. Audio sample rate was 44.1 kHz. I suspected that something within the video-editing/video-exporting process (audio resampling within the app, working or target audio-video format or whatever) caused audio and video to get out of sync. Changed the separately recorded audio to 48 kHz and the audio and video remained in sync.

Some use something called SMPTE as a time code to align an audio file to a video.
Whenever your camera has it, you maybe may use it to align your video to also your MIDI.

Time code works when you chain two devices together while recording, but typically only professional gear can input/output time code.

I've recorded fairly long video along with Pianoteq without drift issues... but not 3 hours. Camera drift is VERY likely to happen after 3 hours, although 6 minutes is still huge. If everything else is correct I would suspect a sampling rate issue there (something other than 48 kHz). If you get your frame rate messed up in any way within your video editor you will get significant drift too.

Julien's idea would definitely be worth checking, I've accidentally bumped tempo without realizing it until trying to match exported audio to a video track. One second off in 10 minutes is quite a lot.

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Are you sure both MIDI files have exactly the same tempo ? I can't reproduce that , I have recorded a very long midi sequence simultaneaously in Pianoteq 6.7.3, Garageband and Reaper, for 34 minutes, and they all are perfectly in sync when I import the Reaper and Pianoteq midi files in Garageband, and also when I import the wav file generated from Pianoteq in garageband.

bump - original post updated at top

Thank you for your update.

Some use something called SMPTE as a time code to align an audio file to a video.
Whenever your camera has it, you maybe may use it to align your video to also your MIDI.

Also, different devices, be it a camera, an audio recorder, or a computer, can easily get out of sync from each other. Some cameras, and even audio recorders don't have great internal clocks.

Not sure what your particular issue is being caused by, so just throwing out some possibilities.

I used a digital stopwatch to time myself playing for exactly 10 minutes, and when I timed the playback from Pianoteq (without exporting to audio) I got an increase of 1 second. (Actual numbers: live playing: 9:59.96, playback: 10:01.00)

I made a video test which became gradually out of sync like before, and another test using Pianoteq as a VST in Garageband, which had no problems, stayed in sync, and passed my stopwatch test.

I appreciate the attention this issue is getting.

-Jordan

Thank you, man.

And julien, I appreciate your having fixed a title bar display of the new EQUALIZER.

Thank you.

But "Export to audio file" seems to be rendering the files at exactly 521.00 microseconds per tick: It's a rounding error!

Good catch, xooorx, this is fixed in Pianoteq 6.7.1 !

It's worth noting that Pianoteq does the right thing when you run it as a VST instrument within a DAW.  The problem is only when you use Pianoteq's standalone export function.

Pianoteq MIDI files specify a division of 960 ticks per quarter note, at a tempo of 500000 microseconds per quarter note.

So that should work out to 520.8333333 microseconds per tick.

But "Export to audio file" seems to be rendering the files at exactly 521.00 microseconds per tick: It's a rounding error!

This might seem a tiny difference but it's enough to drift noticeably out of sync with video within a few minutes, and to be just plain wrong a few minutes after that.

And if the exported audio ever gets mixed with a line recording then it's enough to cause phasing problems right from the start.