Certain videos appear more saturated than in normal media player apps

[frenzibyte]

On the right is o!f and on the left is QuickTime Player:

Video: https://discord.com/channels/90072389919997952/892258907135836212/1297071581230530611 (to be replaced with a sharable video later).

[Joehuu]

Maybe related to ppy/osu#30399. That's talking about image alpha.

[frenzibyte]

That does not seem to be relevant as far as I can see. In fact, I see zero difference between o!f and a media player on the existing test sample video h264.mp4.

[frenzibyte]

Investigations show that since the video is marked with AVCOL_SPC_UNSPECIFIED colorspace, it's looking odd in o!f because it's using these matrix coefficients, whereas forcing it to use the matrix coefficients for Rec. 709 renders the video closer? to correct colours:

I'm still not entirely sure why this video in particular is faulty in o!f while its metadata almost exactly matches the sample video h264.mp4, which I can't notice anything wrong with it. The only thing I can find about this video is that it was exported with Premiere Pro.

[peppy]

Just change it to use rec709 if unspecified and call it a day.

But where are you seeing the "video is marked with"? Are you saying that this differs from the other test video? Your description is unclear.

[frenzibyte]

The other test video also has unspecified colorspace, and using the rec709 matrix for unspecified makes the test video look wrong (yellow/cyan/green colours looks more dimmed).

Test video with master's matrix coefficients:

Test video with the BT709 matrix coefficients (above proposal):

[peppy]

fwiw the owc video also looks different in quicktime vs iina (mpv/ffmpeg based):

[frenzibyte]

The results are actually a bit weird, IINA is incorrect while bare mpv is correct;

Furthermore, I was randomly searching through VLC's code and I stumbled across this:
https://github.com/videolan/vlc/blob/456d7c92575dd226c8b967d312d5a67b4fa8fb55/include/vlc_es.h#L458-L464

Then I compared it with QuickTime Player's behaviour by scaling the sample video to specific resolutions with ffmpeg while keeping the colorspace tag as unspecified, and it turns out QuickTime uses the Rec. 709 colorspace for any video with a width higher than 704 or height higher than 576. I'll push a PR inline with that behaviour seeing that both VLC and QuickTime Player do it (plus or minus implementation details).