Michael:
On 2023-12-27 15:20, Michael Koch wrote:
Am 27.12.2023 um 23:59 schrieb Jim DeLaHunt:
Michael:
On 2023-12-27 13:51, Michael Koch wrote:
...I'm using this command line to print four consecutive random
numbers:
...
I do not have an answer to your question about the behaviour of the
random() function. However, I cannot reproduce your results on my
machine. I get an error complaining about the video filter syntax
instead.
If not on a Windows machine, you may have to encapsulate the filter
thread in double quotes.
Please try this command:
ffmpeg -filter_threads 1 -loglevel repeat -f lavfi -i
color=gray:size=1x1,format=gray -vf
"geq=lum='st(0,0.123);print(random(0));print(random(0));print(random(0));print(random(0))'"
-frames 1 -y out.png
Right you are. Enclosing the filter expression in double quotes, I was
able to reproduce your result. Four numbers printed out, and the first
of them was 0.000000. The remaining three were exactly the same as your
output. That makes those numbers seem not very random.
Interestingly, when I change "random(0)" to "random(0.9)", I get the
identical sequence of four numbers. The behaviour of the parameter is
not the "seed" behaviour that I expect.
The documentation says, "x is the index of the internal variable which
will be used to save the seed/state."
(https://ffmpeg.org/ffmpeg-all.html#Expression-Evaluation). I don't know
what it means by "index of the internal variable", and I don't know what
"save" means. In a function named random(), I expect the parameter to be
used as a seed. I guess this is one of the places where one has to read
the source code.
Apologies for my confusion,
—Jim DeLaHunt
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