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

[Gyan]

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.

Gyan


>
> On Fri, Aug 9, 2019 at 1:08 PM Gyan <ffmpeg at gyani.pro> wrote:
>
>>> On 28-07-2019 01:37 AM, Marton Balint wrote:
>>>>
>>>> On Fri, 26 Jul 2019, Gyan wrote:
>>>>
>>>>> Patch supported by and tested at Google.
>>>> Seems like a huge hack for a decklink issue... ;)
>>>>
>>>> I wonder if there are better approaches to work around this. Like
>>>> dropping all frames until we have a valid signal.
>>> Let's say the scenario is like this,
>>>
>>> Frame #            TC                 Status
>>>       1                   no               dropped
>>>       2                   no               demuxed
>>>       3                   no               demuxed
>>>       4                   no               dropped
>>>       5          04:11:21:04       dropped
>>>       6          04:11:21:05       demuxed
>>>
>>>
>>> We don't want to drop frames before 6; they still should be digitized
>>> (sometimes the TC appears after ~15 frames). But the stored TC needs
>>> to be 04:11:21:04 + (2 - 5) =  04:11:21:01
>>>
>>>> How is this repoducible? do you have an exact model / signal type /
>>>> TC source requirement?
>> (Anchor for reply)
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