[Cin] The best strategy to render yuv (mpeg, limited range) from yuvj (jpeg, full range)?

[Tarantas]

On Thu, 29 Aug 2024 22:12:38 +0000
Andrea paz <gamberucci.andrea at gmail.com> wrote:

> I don't think YT skips color compression if set directly as YT wants
> it. Anyway it's a complicated and interesting topic and if you do
> tests and find an optimal solution please let me know and I'll put it
> in the manual.

Well, here's my draft if I would write such a manual.

"""
Title: [the subject of this thread actually]

For a historical reasons, almost every piece of video software uses
limited range [...]

But, sometimes you have to deal with files encoded utilizing the full
range. For example, some video cameras encode full range files. The
simplest way to deal with them is just to re-encode in limited range:

  ffmpeg -i input.mp4 -c:v libx264 -preset fast -crf 19 -c:a copy \
    -pix_fmt yuv420p output.mp4

But, this is not an option for you if you're either a perfectionist or
trying to fight color banding.

Color banding is a video artifact that could be visible in smooth areas
of the video.
Here's an example: https://youtu.be/KL8CIZej19o
If you don't see the ugly background, then you don't need to worry
about the whole issue.

Color banding is different from compression artifacts. You can't fight
it just by increasing the bitrate of your video.

Color banding comes from color correction performed too much or in
inaccurate way. And it stacks, so if you faced it, then you should get
rid of dynamic range compression at every step it happens.

Cinelerra has a native full color range support, and you can enable it
via:
Settings -> Preferences -> Appearance -> YUV color range: JPEG
Note how everything will loose contrast and become grey-ish.

But, in this mode, Cinelerra will also render full range video files.
There are two reasons why it could be a bad thing:
 - some video players don't understand what full range is and will play
   these resulting videos with the increased contrast;
 - some image processing software (like YouTube) will re-encode full
   range videos into limited range by compressing the dynamic range and
   making the color banding issue even worse.

That's why you should make a couple of hacks.
First, after your project is done, apply F_colorspace filter at the end
(bottom) of the stack with these options:
 - range: 1
 - irange: 2
Second, in File -> Render -> Video, place this line at the end of big
textfield:
  color_range=mpeg

Since you're already fighting color banding, the good thing is to
32-bit colors in Settings -> Format -> Color model: RGB(A)-FLOAT.
Note this could slow down your playback and rendering.
"""

By the way, if anyone is wondering "why is this guy so obsessed with
such a rare issue" - well, I shoot blurry asphalt, usually misexposed:
https://www.youtube.com/watch?v=B6QukURw_Og
This was the good example where I was clever and minimized the damage.
I have worse and don't want to look at them.

By the way^2 - I just notice the cinelerra manual is the first result
for googling "mpeg color range". Cool!

> However, this is a different matter from what you were asking. You
> could try using ffmpeg from the command line using the option:
> -vf "scale=in_range=jpeg:out_range=mpeg" -pix_fmt yuv420p
> and compare with the result obtained in CinGG to see if there are any
> differences.
> 
> Question: In CinGG, what format and preset do you use for the
> rendering to export to YT?

Nothing fancy really.

File -> Render:
  File format: FFMPEG mp4
  Audio:
    bitrate 0,
    quality 5 (an overkill really, produces ~450 kbit/s AAC, but it's
               still noting compared to video)
  Video:
    bitrate 0,
    quality -1,
    pixels yuv420p,
    in a big field for options:
      crf=25 (for a 4K, must be lower for 1080p)
      preset=fast

This provides a nice gently compressed video for long-time storing and
uploading to YouTube.