[Cin] Suggestion: improve setting for VP9 webm

[Miroslav Rovis]

It's simple, and my wording may not be quite precise, but you guys and gals
will understand.

So, when using the setting in the render window, I figured out that there are
better settings to use than the presets that are offered. And they are simpler
too.

In essence, the Wiki page for VP9 can tell you all:
https://trac.ffmpeg.org/wiki/Encode/VP9 [*]

I have no rendering, actually no Cinelerra opened right now, so, from memory:

It's just b=0, then add crf=31 (or other number), and then row-mt=1, and remove
the min and max settings from the preset.

I did use b=0 (which would correspond to -b 0 in the VP9 wiki page (but I see
only -b:v 0 in the page). And it did work I can tell you.

However, see there around:
"more contemporary CRF-style approach for the final pass to achieve a certain perceptual quality"
and there is -b:v 0 in the second pass.
and around:
"must use a combination of -crf and -b:v 0. Note that -b:v MUST be 0."

Also find:
"FFmpeg added support for row based multithreading in version 3.4, released on
January 25th, 2018. As of libvpx version 1.7.0 this multithreading enhancement
is not enabled by default and needs be manually activated with the -row-mt 1
switch."
which I find works great as well on my systems. They are relatively new:
AMD Ryzen 7 PRO 4750G
and also one:
AMD Ryzen 7 5700G
so if the above maybe would not work well on older machines, then, don't know...

So, this is a suggestion to improve the VP9 webm presets in Cinelerra FFmpeg.
While I am getting better at understanding the source code, I would still
probably be to slow to find it and change it and send a patch myself. Too slow.
And that would take me more time than I can set apart at this time.

Regards!

---
I've been using VP9 (previously VP8) webm a lot. E.g. anywhere you go from:
https://www.croatiafidelis.hr/2022/
or, to take just one sample (4 minutes):
https://www.croatiafidelis.hr/2022/Jazovka/VID-2022-06-22-1034-Jazovka-procesija.webm
It's nothing but motion plugin set up, blur plugin in the bottom video at 100%,
and go render. Then work the audio separately, mux and post. Of course, the
stabilizing is slow, motion plugin takes long to calculate.

But all those people moving can be scrutinized in a lot of detail, as if I
filmed with a mobile phone attached to a good stabilizer, and instead, the
original was a shaky video as ever, because I held the mobile with just my
hand.

Cinelerra can stabilize you videos well. It's worth the time-expensive
learning curve to get to know how to do it.

Here are some comparison videos with both the shaky and stabilized video
(however I've gotten better since then, these are all old, but I have no other
comparisons)

e.g. from:
https://www.croatiafidelis.hr/2019/
the videos e.g.:
https://www.croatiafidelis.hr/2019/Jaska/190824-Jaska-Vukovic-demo-1-stabilize.webm
or from:
https://www.croatiafidelis.hr/2015/Macelj/Macelj-2-cmp.php
the video being:
https://www.croatiafidelis.hr/2015/Macelj/150607-Macelj-HebrangCOMP.webm

-- 
Miroslav Rovis
Zagreb, Croatia
https://www.CroatiaFidelis.hr
my PGP-key:
https://www.croatiafidelis.hr/FCF13245ED247DCE443855B7EA9884884FBAF0AE.asc
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