[Ardour-Users] "Extract LTC from audio and align video" menu option missing from "Transcode/Import Video file" popup
robertlazarski at gmail.com
Tue Apr 3 19:43:07 PDT 2018
On Mon, Apr 2, 2018 at 3:24 PM, Robin Gareus <robin at gareus.org> wrote:
> Hi again,
> On 04/02/2018 09:52 PM, robertlazarski . wrote:
> > However, the video and audio are out of sync. If I press the F8 record
> > button before I start the video, the audio comes in early. If I press the
> > F8 record button after I start the video, the audio comes in late.
> That sounds like both recorders are free-running.
Might be, I tried using time of day timestamps and it didn't help.
> Are you using a common timecode generator that syncs the two devices?
> Where does the LTC that's recorded on the camera come from?
> What timecode does the audio-recorder use to set BWF information?
All timecode comes from one source: The F8. More details below.
> > [..]
> > I spent some more time reading the docs. In Xjadeo I couldn't get the
> > offset "+" and "-" buttons to work.
> When Ardour launches xjadeo, most of the direct interaction with Jadeo
> is disabled. It becomes a dumb display under Ardour's control.
> You can drag/drop the video in Arodur's video-timeline to align it,
> xjadeo will follow, but that should not be needed.
> If the timecode on the video (LTC) matches the timecode of the audio
> (BWF), everything will just line up all by itself.
> Note that both audio and video may import at some late position in the
> timeline. e.g. at 14:00:00:00 and may not be visible with default
I tried zooming in and out and didn't see an obvious misalignment.
> > [..]
> > the "space" bar starts and stops as expected.
> Yes, those keys are forwarded to Ardour.
> > I tried exporting from Ardour to video and it took about 9 hours -
> > it generated an export.avi with just audio - no video and "seek" seems to
> > not work in mplayer.
> Wow. What range did you export? a 12+ hour video?
I need to watch out for blank video space in the imports, I didn't expect
> > I don't understand yet, how to match the timestamps I see from ltcdump on
> > the MP4 converted to WAV, and what I see from bwftool on the F8 generated
> > WAV. I am still learning.
> Ardour should do that for you, but if you do want to do this manually:
> I don't know bwftool, `sndfile-info --broadcast` prints the raw data:
> audio-samples since midnight.
> e.g. if you started recording audio at 8am sharp at 48kHz. it'll print
> show 4147200000 ( 8 hours * 3600 seconds/hour * 48000 samples/second)
> You can do the reverse and find the time when given audio-file was
> recorded. the 4147200000 would translate to 08:00:00:00
> As for video, use ltcdump and take the first found timecode.
> Timecode | Pos. (samples)
> 07:58:00:00 | 0 1919
> 07:58:00:01 | 1920 3839
> 07:58:00:02 | 3840 5759
> above means at audio-sample "0" (beginning of the video) it's
> 07:58:00:00. In this example the video-recording was started 2 mins
> before audio (08:00:00:00).
On my latest files I am attempting to use "time of day" timestamps in the
timecode, using the F8 "Int RTC" mode.
The sync error pattern I am noticing, is the first entries of LTC in the
MP4 file seem to be missing or corrupted. The POS from ltcdump never starts
at zero. When I open the raw MP4 I see no such obvious problem.
In a nutshell, there is a 12 second delay of audio in the video I see in
Xjadeo, that seems to correspond with the 12 seconds missing in the LTC on
I am seeing the same pattern on every file. Hopefully the shell output
makes sense. I see this "DISCONTINUITY" message in every file I create,
could that be my problem?
One other thing I notice, is the timecode in the Ardour UI starts at zero,
not time of day.
/home/iksrazal> sndfile-info -b F8.wav
Version : libsndfile-1.0.25-exp
Description : SPEED=29.970D
Originator : ZOOM F8
Origination ref :
Origination date : 2018-04-03
Origination time : 18:31:09
Time ref : 0x0bebdd5f1 (66669.002354 seconds)
BWF version : 1
Coding history : A=PCM,F=48000,W=24,M=multi,T=F8;VERSION=1.10;1:1 0 0 R
1 00;2:1 0 0 CNTR 00;3:0 0 0 CNTR 00;4:0 0 0 CNTR 00;5:0 0 0 CNTR
00;6:0 0 0 CNTR 00;7:1 0 0 CNTR 00;8:1 0 0 CNTR 00;L:0 1 0 CNTR
00;R:0 1 0 CNTR 00;
/home/iksrazal> ltcdump phone_video_with_ltc.wav | head
Note: This is not a mono audio file - using channel 1
#User bits Timecode | Pos. (samples)
00000000 18:31:21.29 | 2639 4239
00000000 18:31:22.00 | 4240 5841
00000000 18:31:22.01 | 5842 7442
00000000 18:31:22.02 | 7443 9044
00000000 18:31:22.03 | 9045 10646
00000000 18:31:22.04 | 10647 12247
00000000 18:31:22.05 | 12248 13849
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