[Ardour-Users] "Extract LTC from audio and align video" menu option missing from "Transcode/Import Video file" popup

robertlazarski . robertlazarski at gmail.com
Thu Apr 5 06:32:13 PDT 2018

On Wed, Apr 4, 2018 at 8:27 PM, Chris Caudle <chris at chriscaudle.org> wrote:

> On Wed, April 4, 2018 5:00 pm, robertlazarski . wrote:
> > Its a nasty signal. It might be severally clipping but I don't have
> meters
> > on it.
> I forgot you had an external interface.  Since it is USB, you could
> connect it to your computer and use the meters in Ardour to check the
> level of the time code signal from the F8, and adjust it until there is
> plenty of headroom.

I might try that if I am still stuck much longer. Its a good idea.

> See below.
> > Seems like its [i.e. phone recording] using AAC
> I checked using the command line ltc tools, and I can create a wav file,
> convert to AAC using the old Nero encoder, decode using the Nero decoder,
> and the ltcdump output is identical between the original wav file and the
> wav->aac->wav path.
> However, the original wav file creates the LTC with a max level of -18dB
> FS, and the encoded/decoded version of the same has a max level of -15 dB
> FS.  I don't know if that is called out in the AAC spec anywhere or if
> that is peculiar to the Nero AAC encoder/decoder pair, but very curious.
> Be sure to leave plenty of headroom in the original in case that is some
> kind of common behavior in the AAC encoder or encoder/decoder pair.
> You can see the max level with sndfile-info if you leave out the "-b"
> argument, it will print  information about the audio data instead of the
> BWF metadata.
> --
> Chris Caudle
On the files I just created today I see:

 /home/iksrazal> sndfile-info output_audio.wav  | grep -i db
Signal Max  : 32768 (0.00 dB)

And if I learned how this works right, 3212 samples is 3212/48000 = 66ms.
That's not my problem if I understand correctly.

 /home/iksrazal> ltcdump output_audio.wav | head
Note: This is not a mono audio file - using channel 1
#User bits  Timecode   |    Pos. (samples)
00000000   06:05:34.24 |     3212     4683
00000000   06:05:34.25 |     4684     61nc 54
00000000   06:05:34.26 |     6155     7626
00000000   06:05:34.27 |     7627     9097
00000000   06:05:34.28 |     9098    10571
00000000   06:05:34.29 |    10572    12040

I posted my files to see if that helps understand my sync problem. At this
point my theory is the amount of sync delay I see, is pretty much exactly
the delay between pressing start on the F8 and then a few seconds later
pressing start on the phone video. I am seeing around a 6 second delay in
this example.

In the video, I am using a chase light step sequencer to trigger the drum
beat, which probably is more useful than the brief piano chords i tried to
make apparent by my arm movements. I start the video filming my other phone
with a wall clock running, to help show what's going on. The F8 internal
clock does not sync to NTP or GPS best I can tell so I eye balled the F8
date setting the best I could.

Also, I could be doing something wrong in Ardour. All I am doing is Session
--> import (F8 wav) . then Session --> open video.

MP4 phone video with LTC, since this is a public link I advise extreme
caution opening any file with LTC.


F8 BWF wav with 4 tracks. The piano seems a little low compared to the drum
machine, will try to fix that next time.


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