[FFmpeg-user] ffmpeg architecture question

Mark Filipak markfilipak.windows+ffmpeg at gmail.com
Fri Apr 17 22:55:52 EEST 2020

On 04/17/2020 02:46 PM, Paul B Mahol wrote:
> On 4/17/20, Mark Filipak <markfilipak.windows+ffmpeg at gmail.com> wrote:
>> Another cogent point:
>> Suppose I put 'datascope' before a filter that would pass the original frame
>> (say, based on a
>> color), but that the filter won't pass the 'scope' image (because it doesn't
>> contain that color). I
>> haven't tried it, but I'll bet that the 'scope' image doesn't appear at all
>> and that the frame is
>> dropped.
>> (Note that if I moved the 'datascope' to after the filter, it would work as
>> expected.)
>> Supposing that I'm correct, and considering the prior experiments that I did
>> conduct, the
>> non-recursive nature of ffmpeg filter complexes is an important
>> architectural feature that's not
>> documented.
>> Understand that I'm not criticizing ffmpeg. ffmpeg works how it works and
>> that's fine. It just
>> doesn't work like an oscilloscope. It could have been designed to work like
>> an oscilloscope, but it
>> wasn't. That's okay, but it really should be documented.
>> Do you agree, Paul, or am I mistaken?
> Tried this simple command?
> ffmpeg -f lavfi -i testsrc2 -f lavfi -i testsrc -lavfi
> "[0:v]select='mod(n,2)'[a];[1:v]select='1-mod(n,2)'[b];[a][b]interleave"
> -f null -
> Interleave filter use frame pts/timestamps for picking frames.

The interleave filter is not the issue, Paul. Your response is off-topic. Nonetheless, I'll try to 
respond constructively.

Regarding your command line, I read https://ffmpeg.org/ffmpeg-devices.html#lavfi. I didn't 
understand it. That 'said', your command line appears to alternate frames: frame 0 from testsrc, 
frame 1 from testscr2, etc. But to directly answer *your* question: No, I have not "Tried this 
simple command".

Since you have not responded to my "Do you agree" questions, and have instead presented me with some 
sort of puzzle (or test), well, I don't know what to think.

If there's one thing I've learned about you, Paul, it's that you don't answer simple questions with 
simple answers.

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