[linux-audio-user] SMPTE timecode reader

plutek plutek at infinity.net
Mon Dec 18 22:13:47 EST 2006


On 12/18/2006 09:44:11 PM, Robin Gareus wrote:
> Hi!
> 
> > cool to hear it is (or was) on the xjadeo todo list,
> 
> it still is. one might get the idea to play a video file along to an
> live audio-LTC, but no one requested that feature yet ;-) I guess it
> could be useful for making video-walls using "old" computers without
> MIDI and netjack...
> 
> > i've needed this stuff recently while doing
> > audio for live video shoots, just so we can all work from (and
> record) a
> > common timecode reference, and confirm while shooting that we are
> > actually locked.
> 
> I'm confused by "live video shots", are you editing (offline) or you
> were monitoring (online/live)? mmh. OTOH it does not matter, does it?
> In case it's during shooting: Are you feeding a camera generated LTC
> into the the DAT, or some external generator into both the camera(s)
> (which also records audio) and the HDR/DAT?

during shooting. we were going to feed the studio64-xtc LTC to both the  
cameras and ardour, but had trouble locking cameras to that code -- i  
actually think this may have been a problem with the feed from my end,  
but we didn't have time to debug it. we ended up feeding  
camera-generated LTC into ardour in realtime while shooting.

> -> how good/noisy is the LTC signal?
> -> is it raw audio data or has it been resampled/transcoded. (lossy MD
> or mp3 recording ??)

i don't know how good the camera-generated LTC is. i have not yet tried  
to lock the studio64-xtc to that, but will try tomorrow.

> 
> 
> > yes, i can generate, but i cannot parse an incoming stream. i also
> have
> > no way of knowing what time i'm spitting out (unless i also send MTC
> and
> > lock i.e. ardour to it), since my generator (an old opcode
> studio64-xtc)
> > just runs with no display of where it is. it CAN lock to incoming
> LTC,
> > but again i must tell it to transcode to MTC and then lock software
> to
> > it in order to know what's going on.
> 
> don't get started on that windows machine... I've got some old files
> where I know the timecode for reference (25fps).  Hardware is
> interesting for noise analysis (input) and to verify if proprietary
> boxes can lock to the signal that "libltcsmpte" will generate.
> 
> If I can read my own files, I'll try some of yours. Could you email or
> upload a minute of example LTC (wav or aiff - gzip ) or maybe better
> make that more files: clean and noisy :-) what is your usual
> framerate?

sure, i'll generate some samples, and also prepare a sample of what i  
recorded from the camera. the video producer i'm working with now is  
using 29.97 non-drop, but i'll send a range of frame rates

> 
> when the parser works it'd be interesting to set up a loop: Can your
> studio64-xtc lock to incoming LTC and output LTC (w/o you installing
> windows)?

i'll check tomorrow. i think so. i may just fire up my wife's old win95  
laptop anyway, and play with MTC transcoding, just for the fun of it.  
yes, i'm up for beta testing. i don't have cameras available to play  
with, but i have a few computers here to sync together, along with the  
studio64-xtc.

> that should be good enough for preliminary tests. In
> January
> I can get my hands on a scope..
> 
> I'm leaving for Austria tomorrow, and be will online again at the
> Chaos
> Communication Congress in Berlin after x-mas.

cool. great to see this moving forward. it would be very cool to be  
able to lock to LTC for post-production on this project.

you may have noticed that erik de castro lopo has stepped into the ring  
as well.... wow; a flurry of activity!

i'll be in touch about samples.

.pltk.


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