i forgot what "-q:v 3" does in image resizing

[sommers]

SET "F4=-q:v 3"
SET "GG=-sws_flags lanczos"
::SET "GG=-sws_flags bicubic"
SET "ZZ1=-vf scale=w=800:h=600:force_original_aspect_ratio=decr ease %GG%"

ffmpeg.exe -y -i "aaaa.bmp" %ZZ1% %F4% "aaaa-.jpg"

rem -i means input file that is "aaaa.bmp"

does this -vf mean video filter? and -af mean audio filter?
you must choose either -vf OR -af on every task, right?

i forgot what F4 does, -q:v is usually associated with audio quality but in jpg2000 explanation, it says video quality, could someone add some more explanation?
one thing i can understand is, since the output is jpg, -q:v could be the JPG quality control

in 1 to 10 scale what does "3" represent?
-q:v 1 best quality, poor compression rate
-q:v 2
-q:v 3 maybe my default
-q:v 4
.
.
.
.-q:v 10 poor quality, best compression rate

[jagabo]

There's a space between the vf settings and -q:v so it has nothing to do with the scaling. It's the quality of the jpg video encoding.

[sommers]

>There's a space between the vf
like this -v f, but there were no commands like this in help, all examples used were -vf stuck together

>-q:v so it has nothing to do with the scaling. It's the quality of the jpg video encoding.
of course not, -q indicated that it would start a new command that would be added to the line, and i did that

-i "aaaa.bmp"
-vf scale=w=800:h=600:force_original_aspect_ratio=decr ease
-sws_flags lanczos or
-sws_flags bicubic"
-q:v 3 "output.jpg"

> It's the quality of the jpg video encoding.
so this syntax or command format is correct? -q:v 3 "output.jpg"
i hope see your syntax example


-q:v 1 best quality, poor compression rate
-q:v 2
-q:v 3 maybe my default
-q:v 4
.
.
.
-q:v 10 poor quality, best compression rate
and one of the example goes
.-q:v 1000

so i lost my understanding

[jagabo]

Valid values for q range from 1 (highest quality, largest file size) to 31 (lowest quality, smallest file size). If you enter a value larger than 31 the encoder will use 31.

[sommers]

ECHO -q:v varies from 1 to 31
ECHO 1 : best quality poor compression
ECHO 3 : my original selection (maybe too good)
ECHO 4 : my current selection (closer to VSO's quality=80%)
ECHO 10 : still kind of poor (i still see smudging)
ECHO 31 : poor quality best compression (unacceptable)

thanks i got it
ffmpeg.exe is only the one that i know it can convert webp to bmp
so i dont need to install a memory resident webp translator or some plugins