[LAD] SMPTE and jackd

Robin Gareus robin at linuxaudio.org
Tue May 8 14:20:00 UTC 2012

On 05/08/2012 04:11 PM, Egor Sanin wrote:
> On 5/8/12, Robin Gareus <robin at gareus.org> wrote:
>> s/drop/skip/
> Yes, correct.
>> JACK-transport timecode (as returned by jack_transport_query())
>> increases in steps of the period size. It depends on the application
>> what to make with this.
> Yes, exactly, see below.
>> jack_frame_time() OTOH estimates the time and includes the offset
>> jack_frames_since_cycle_start(); but I don't know how accurate this is.
> Yeah, I think it's best to work with jack frames as returned by
> jack_transport_query().
>> Where does the SMPTE come into play? MTC?
> Yes, I'm writing a jack transport to MTC converter for syncing some
> things.  It's embarrassingly infantile code at the moment, but I'm
> working on it, it's also my first jack program.  It displays SMPTE
> time in a console at the moment.
> http://sourceforge.net/projects/jackmtc/

FWIW, libltcsmpte.sf.net includes two tools in the example-code section
that create MTC (both ALSA-MIDI:jack2amidi as well as JACK-MIDI:
jack2jmidi) from jack-transport:

They are - however - skipping frames if the JACK period-size large.

> I know there's MTC code in xjadeo (and qtractor or some other DAWs, I
> think), but I want a standalone console tool.  Admittedly, I haven't
> looked at xjadeo code in detail, I'm trying to wrap my head around the
> concepts first.
> Thanks.
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