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

robertlazarski robertlazarski at gmail.com
Fri Apr 20 09:49:06 PDT 2018

On Fri, Apr 20, 2018 at 8:24 AM, Chris Caudle <chris at chriscaudle.org> wrote:

> On Wed, April 11, 2018 8:21 am, Chris Caudle wrote:
> > And the app is set at 29.97fps? I'm still confused about why ffmpeg is
> > flagging the video file as 29.89fps.
> I found a useful program called mediainfo available in the Fedora
> repositories.
> Original project seems to be here:
> https://mediaarea.net/en/MediaInfo
> CLI and GUI versions available.
> The report from mediainfo for  the phone video contains this info on frame
> rate:
> Frame rate mode                          : Variable
> Frame rate                               : 29.892 FPS
> Minimum frame rate                       : 16.411 FPS
> Maximum frame rate                       : 30.344 FPS
I am going to check that program out as its clearer on what's going
compared to what I doing now, thanks for the tip.

I've delayed my response because I have been doing some bash script hacking
with ltcdump that I almost have working. Hours turned into days :-) . Its
not that big of a script and I will have more to say on that soon.

> I'm not sure how variable frame rate works in h264 encode/decode,
> presumably it has to be converted to a consistent frame rate for playback,
> but I'm not  sure.
> Perhaps that is confusing the video file import, I have only ever worked
> with video files with constant frame rate.

The phone problem with Ardour was indeed because it was a variable rate
issue. I was able to fix it with this command. And then Ardour was fine
with it.

HandBrakeCLI -i ../motox_in_file.mp4 --cfr -r 29.97 -o fixedmoto.mp4

> I know you said you were purchasing some kind of small video camera, I
> have not compared prices lately but it might be useful to see what older
> SLR cameras with video capability are selling for on the used market.
> 1920x1080 is only around 2M pixels, maybe there are a lot of 2M - 6M pixel
> cameras getting sold cheaply because all the photo people want the new 20M
> pixel hotness.  DSLR also has the advantage you can switch out for better
> or at least more appropriate lenses at some point if you want (telephoto,
> wide angle, different aperture capability, etc.).  I guess verify that the
> files from a DSLR work like you need first, my wife's SLR doesn't do video
> so I can't check with that model.
So I was able to get the Q8 working with Ardour too. The Tentacle Sync LTC
generator also works fine and I'm really happy with it.

TBH I think phone cameras are "good enough" for this project, but it
requires a usb interface and while the Irig DUO works ok I just like the Q8
workflow more. The camera on the Q8 is nothing special but the audio is
fantastic. To be clear my priority is good audio and then whatever video
that comes with it is ok for me.

My main problem finding a camera is something with good audio via XLR
inputs. Audio only recording is a nice plus. The Q8 right now is $350 and I
couldn't find anything else with XLR inputs under $1000. The main issue
with the Q8 right now is that its from 2015 and I expect a new model soon.
Even still I am probably going to buy a second one.

> Chris Caudle
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So about these scripts I am writing ...

I can sync both cameras fine individually. Ardour and Xajdeo only supports
one video at at time. Best I can tell the typical workflow using Ardour for
multiple cameras, has a video software editing step in between recording
and Ardour.

However I googled and I couldn't find a Linux based UI that can read LTC -
besides XJadeo but for multiple videos that's not the right tool? I
installed a couple things and couldn't figure out how to read ltc. There
must be something people use for multiple cameras that contain ltc though,
any hints appreciated.

In the meantime I thought it would be relatively easy to segment the videos
via ffmpeg and then pipe that into ltcdump. Using bash (or any language)
for timestamps parsing is tricky though so I'm debugging that now. Soon
I'll either get stuck or show what I have working.

Kind regards,
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