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

[Mark Filipak]

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.

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