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

Robin Gareus robin at gareus.org
Mon Apr 2 14:24:42 PDT 2018

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.

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?

> [..]
> 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

> [..]
> 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 - however
> 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 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).


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