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

robertlazarski . robertlazarski at gmail.com
Mon Apr 2 12:52:26 PDT 2018

On Sun, Apr 1, 2018 at 2:20 PM, Robin Gareus <robin at gareus.org> wrote:

> On 04/01/2018 09:51 PM, robertlazarski . wrote:
> > I recently posted a question about LTC on the LAU mailing list, and was
> > given some advice to try the Ardour "Extract LTC from audio and align
> > video" option. However, I don't see that option in the "Extract audio"
> drop
> > down box. I see two optons:"do not extract the video" , and an option for
> > "AAC" .
> It's a Checkbox below the dropdown.
>    see http://robin.linuxaudio.org/tmp/extract_ltc.png
> It's pretty basic. It uses the first (left) audio channel and ties to
> decode LTC.  It uses LTC frames from the beginning of the stream to
> align the start of the video.
> Check Menu > Window > Log, LTC messages currently go there.
> Since you compile from source, you can also enable various debug
> messages in  libs/ardour/ltc_file_reader.cc
I found the checkbox, and it opened up Xjadeo with my MP4 video with the F8

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.

I spent some more time reading the docs. In Xjadeo I couldn't get the
offset "+" and "-" buttons to work.

Some "User Interaction" commands do work, the "i" command displays S: E: L:
timestamps but so far I am not sure what that means. They do not change
values when playing the video. The "enter" command does bring me to
beginning of the video, the "space" bar starts and stops as expected.

So I'm not sure on the next step to sync?

In Xjadeo I do notice the FPS is 29.917 and it matches what ffmpeg says the
original MP4 video file uses. The LTC out from the F8 is set at FPS 29.97
in "Int free run" mode.

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.

hope that helps,
> robin

 I see your name a lot in the code and man pages, thanks for helping a
newbie! I have your ltcdump command installed if that would be helpful. I
had to convert the MP4 file to WAV to use it.

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.

Kind regards,
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