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

[Marton Balint]

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.

Regards,
Marton