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

[Gyan]

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