[FFmpeg-devel] [PATCH] avdevice/decklink: add option to drop frames till timecode is seen

[Marton Balint]

On Wed, 13 Nov 2019, Ilinca Tudose wrote:

> My previous email was incorrect about "-wait_for_tc 1". The 2 commands used
> were:
>
> (1)
> ffmpeg -loglevel trace  -timecode_format rp188any  -wait_for_tc 1 -f
> decklink -probesize 15M -analyzeduration 5M -i "DeckLink Quad (1)" -t 30
> -preset veryfast output.mov
>
> (2)
> ffmpeg -loglevel trace  -timecode_format rp188any  -wait_for_tc 1 -f
> decklink -i "DeckLink Quad (1)" -t 30 -preset veryfast output.mov
>
> The second command is the one that produced 1 frame offset in 3 of the
> captures. The first command had 0 frames offset for all files tried.

These two command lines are only different in probesize and
analyzeduration. I don't understand how these two options can make any
difference regarding the TC offset. Can you figure out which one actually 
causes the issue?

Thanks,
Marton


>
> On Wed, Nov 13, 2019 at 6:30 PM Ilinca Tudose <ilincat at google.com> wrote:
>
>> Hi,
>>
>> We tested this with several types of tapes. The results are as follows:
>>
>> Out of 58 captures on Betacam tapes 55 had 0 frame offset and 3 had an
>> offset of 1 frame. All 3 were captured using the flag "-wait_for_tc 1".
>> Out of the 58 captures roughly half were captured with and half without "-wait_for_tc
>> 1".
>>
>> Out of 26 HDCAM captures (50/50 with/without "-wait_for_tc 1") all 26 had
>> 0 TC offset.
>>
>> Let me know if there's any questions re testing. The testing setup is the
>> same as previously mentioned.
>>
>> Thanks,
>> ilinca
>>
>> On Wed, Nov 13, 2019 at 5:40 PM Gyan <ffmpeg at gyani.pro> wrote:
>>
>>> As suggested in the review of an earlier patch*, this one drops frames
>>> till a TC is seen.
>>>
>>> Testing results to follow.
>>>
>>> Thanks,
>>> Gyan
>>>
>>> *https://patchwork.ffmpeg.org/patch/14081/
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>>
>>
>>
>>
>
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