[FFmpeg-devel] [PATCH] avdevice/decklink: adjust for timecode lag

[Ilinca Tudose]

Hi Marton,

I want to confirm that we get correctly synced TCs when leaving out the
format_code parameter and using an ffmpeg build from head (not with Gyan's
patch). However, I was under the impression that we need the format_code so
that we can capture different content types, in the original format. For
example multiple frame rates or interlaced content. How would we set this
up if we are not using format_code? Is this identified automatically?

Thanks,
ilinca

On Sat, Aug 17, 2019 at 6:06 PM Gyan <ffmpeg at gyani.pro> wrote:

>
>
> On 17-08-2019 09:21 PM, Marton Balint wrote:
> >
> >
> > On Sat, 17 Aug 2019, Gyan wrote:
> >
> >>
> >>
> >> On 17-08-2019 08:42 PM, Marton Balint wrote:
> >>>
> >>>
> >>> On Wed, 14 Aug 2019, Marton Balint wrote:
> >>>
> >>>>
> >>>>
> >>>> On Wed, 14 Aug 2019, Gyan wrote:
> >>>>
> >>>>>
> >>>>>
> >>>>> On 09-08-2019 04:59 PM, Ilinca Tudose wrote:
> >>>>>> Hi Marton,
> >>>>>>
> >>>>>> The issue with the out of sync TC was reproducible on all tapes
> >>>>>> and decks
> >>>>>> that we tested. I don't have the exact number now, but a few
> >>>>>> dozens, less
> >>>>>> than 100. They all had between 7 and 17 frames out of sync. We
> >>>>>> were not
> >>>>>> able to obtain anything more in sync than 7 frames.
> >>>>>>
> >>>>>> The TC sync was tested by setting up the deck to "burn" the TC
> >>>>>> with the
> >>>>>> image while capturing the content with TC through ffmpeg. We then
> >>>>>> play the
> >>>>>> file in a player that supports timecodes and compare the
> >>>>>> burned-in TC with
> >>>>>> the one captured in the metadata.
> >>>>>>
> >>>>>> We used Decklink quad 2 and several Sony decks: J30, J3, JH3. We
> >>>>>> tested on
> >>>>>> multiple decks from each model and confirmed the issue was
> >>>>>> present + that
> >>>>>> Gyan's patch seemed to fix it. We have used several types of
> >>>>>> Betacam tapes
> >>>>>> and HDCAM tapes. I can not comment on whether this is the best
> >>>>>> solution,
> >>>>>> but can confirm it works.
> >>>>>>
> >>>>>> Let me know if you need more info.
> >>>>>>
> >>>>>> Thanks,
> >>>>>> ilinca
> >>>>>
> >>>>> Ping.
> >>>>
> >>>> Sorry, I need a bit more time to investigate.
> >>>
> >>> OK, I did a couple of tests myself for HD and SD pal signals, and it
> >>> seems to me if signal autodetection is used, so no format_code is
> >>> specified then timecode is readily available in the first frame. I
> >>> was using BlackMagic SDK 11.1 for testing by the way. Can you
> >>> confirm the same behaviour with your setup?
> >>
> >> So, were you able to reproduce the issue _with_  format_code specified?
> >
> > I was able to reproduce the part where after starting the capture the
> > decklink device records empty frames (with flag
> > bmdFrameHasNoInputSource set) for a couple of frames.
> >
> > I was not able to reproduce the part where the timecode was earlier or
> > later available then the first frame of the useful video signal.
>
> Ok, thanks. I'll get back when I have more info.
>
> Gyan
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-- 

---
Ilinca Tudose | Technical Solutions Consultant, Digitization Operations |
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