[FFmpeg-user] Decombing via screening - 'tblend' bug (?)

[Paul B Mahol]

On 4/15/20, Mark Filipak <markfilipak.windows+ffmpeg at gmail.com> wrote:
> On 04/15/2020 05:00 AM, Paul B Mahol wrote:
>> On 4/15/20, Mark Filipak <markfilipak.windows+ffmpeg at gmail.com> wrote:
>>> On 04/15/2020 04:25 AM, Paul B Mahol wrote:
>>>> On 4/15/20, Mark Filipak <markfilipak.windows+ffmpeg at gmail.com> wrote:
>>>>> Request for bug confirmation is included.
>>>>>
>>>>> Correction: I had datascope in #2 just 1 time. I don't know how it got
>>>>> into
>>>>> the original post twice.
>>>>> Sorry. - M.
>>>>>
>>>>> On 04/14/2020 10:24 AM, Paul B Mahol wrote:
>>>>>> On 4/14/20, Mark Filipak <markfilipak.windows+ffmpeg at gmail.com> wrote:
>>>>>>> In the command line below,
>>>>>>>                    I will eventually insert a screen maker --+
>>>>>>>                                                              ¦
>>>>>>> separatefields,scale=height=2*in_h:sws_flags=neighbor,--HERE--,tblend=normal[D]
>>>>>>>
>>>>>>> but first, I need to persuade 'tblend' to accept the 2 frames made by
>>>>>>> 'separatefields' (and scaled
>>>>>>> by 'scale').
>>>>>>> But as you can see in the next section (extracted from the log),
>>>>>>> though
>>>>>>> the
>>>>>>> 'height=2*in_h'
>>>>>>> directive works (i.e., the 1920x540 frames from 'separatefields' are
>>>>>>> scaled
>>>>>>> to 1920x1080), ffmpeg is
>>>>>>> not happy. Is it because the SARs don't match? How can I overcome
>>>>>>> that?
>>>>>>> Thanks!
>>>>>>
>>>>>> Insert setsar=1 after scale?
>>>>>
>>>>> Thank you, Paul. It works. I apologize for not finding that solution on
>>>>> my
>>>>> own ...how embarrassing.
>>>>>
>>>>> Next problem: 'tblend' appears to be malfunctioning.
>>>>>
>>>>> "The tblend (time blend) filter takes two consecutive frames from one
>>>>> single
>>>>> stream, and outputs the
>>>>> result obtained by blending the new frame on top of the old frame."
>>>>>
>>>>> #1 - This works as expected:
>>>>> ffmpeg -i IN -filter_complex "telecine=pattern=5, split[A][B],
>>>>> [A]select='not(eq(mod(n+1\,5)\,3))'[C], [B]select='eq(mod(n+1\,5)\,3)',
>>>>> datascope=size=1920x1080:x=45:y=340:mode=color2[D], [C][D]interleave"
>>>>> OUT
>>>>>
>>>>> #2 - This malfunctions:
>>>>> ffmpeg -i IN -filter_complex "telecine=pattern=5, split[A][B],
>>>>> [A]select='not(eq(mod(n+1\,5)\,3))'[C], [B]select='eq(mod(n+1\,5)\,3)',
>>>>> separatefields,
>>>>> scale=height=2*in_h:sws_flags=neighbor, setsar=1, tblend,
>>>>> datascope=size=1920x1080:x=45:y=340:mode=color2, [C][D]interleave" OUT
>>>>>
>>>>> #1 brings up datascope in frames (n, zero-based): 2 7 12 17 etc., as
>>>>> expected.
>>>>> #2 brings up datascope in frames (n, zero-based): 4 7 10 13 etc.
>>>>>
>>>>> Another clue is:
>>>>> #1 OUT has 598 frames.
>>>>> #2 OUT has 716 frames.
>>>>>
>>>>> Would someone who has the latest nightly build kindly confirm this. I
>>>>> can
>>>>> supply the test video --
>>>>> contact me off-list.
>>>>
>>>> You still can not read documentation? Why?
>>>>
>>>> interleave filter simply picks frames from several streams.
>>>> This is obviously explained in documentation.
>>>> tblend filter blend successive frames, this is obviously different
>>>> from interlace filter as that will not drop any frame like interlace
>>>> does.
>>>
>>> Look at my command lines again. Here, I'll give you filtergraphs:
>>>
>>> #1
>>> telecine -> split -> select (n+1%5!=3) ---------------------------->
>>> interleave
>>>                     -> select (n+1%5==3) ---------------------------->
>>> 598 frames (correct)
>>>
>>> #2
>>> telecine -> split -> select (n+1%5!=3) ---------------------------->
>>> interleave
>>>                     -> select (n+1%5==3) -> separatefields...tblend ->
>>> 716 frames (malfunction)
>>>
>>> 598*4/5 = 478 frames (upper 'select')
>>> 598*1/5 = 119 frames (lower 'select')
>>> 119*2 = 238 frames (output of 'separatefields')
>>> 238/2 = 119 frames (what output of 'tblend' is supposed to be)
>>> 238 frames (what output of 'tblend' actually is)
>>> 478+238 = 716 frames (output of 'interleave' showing that 'tblend'
>>> malfunctions)
>>>
>>
>> tblend works fine, you obviously do not know what you doing.
>>
>> Given frames: A B C D E F G:
>>
>> tblend gives this output: AB BC CD DE EF FG, so original number of
>> frames in input minus one.
>
> Are you even looking at the command lines?
>
> #2
> telecine -> split -> select (n+1%5!=3) ---------------------------->
> interleave
>                    -> select (n+1%5==3) -> separatefields...tblend ->
>
> 'telecine' input (IN) is      A B C...
> 'telecine' output is          A A AB B B ... (modulo 5) ...frame 2 is combed
> upper 'select' output is      A A __ B B (n+1%5!=3)     ...progressive
> frames
> lower 'select' output is      _ _ AB _ _ (n+1%5==3)     ...combed frame
> 'separatefields' output is        AB AB                 ...2 frames (1/2
> height)
> 'scale=height=2*in_h' output is   AB AB                 ...2 frames (full
> height)
> 'tblend' output is supposed to be AB                    ...1 frame
> OUT is supposed to be         A A AB B B                ...598 frames
> OUT is                        A A AB AB B B             ...716 frames
> Conclusion: 'tblend' is outputting 2 frames instead of 1 frame.

And that is completely correct for filter to do.

If you not happy with that, write own code instead.

>
> Of course, since I can't read and I'm always wrong...
>
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